ESA pre Jan 13

Please can anybody help. I was on DLA on high rate mobility since 2009 with a life time award. This month I had my re assessment for PIP. I Have been awarded standard rate mobility on pip now, although I still suffer from and receive treatment for long term severe rheumatoid arthritis.
However, my question is this. Today I got a letter from DWP to notify me I will no longer qualify for my motability car as only awarded standard rate (no surprise there!!) But also on same day received a letter called 'Notifiction of Local Compliance Telephone Interview' for the ESA I have been on pre 2013 and applied under contribution based esa as I had given up work due my I'll health. I had worked all my life from aged 16 to aged 45. I was placed in pre 2013 ESA support group where I have been ever since. I have not worked since and do not claim a pension as my work pension doesn't kick in until I am 60 and my state pension when I am 67. Why have I been sent this letter asking for a telephone interview asking for personal information. I almost thought this letter could be a scam?? Is it legit? I have tried ringing the number but it always goes a voice message
. Have I been sent this because I have just had a dla to pip medical?? This is so stressful. I can't see why I have suddenly been sent this letter asking for so much financial information? Help please.

Thank you Gordon for your reply. I am still worried as although it is a telephone interview the later states I am supposed to have any of the following documens for me and my partner (husband of 32 years in my case) as follows;
Bank Statements for current accounts deposit accounts bank and building society, isa savings premium bonds, any land or property other than where I live (we don't have any other land or property and have lived at our current address for 26 years ??) and Immigration status??? I am British born ?? Wage slips or earnings?? I haven't worked and have no wages or pension being paid??
Also the contact number on the letter is 07771 975196. This number goes to a voicemail. Is this a legitimate number as my understanding is numbers beginning with 07 are a mobile number?
I am worried in case this is a scam letter asking for all these financial information and if it is legitimate why I have been sent it.?
I have all my paperwork right back from my original application, but it is pre Jan 2013. I received my entitlement letter this April that confirmed I was on contribution based esa and I was in the support group. Apart from these entitlement letters with any change of new rates I have never received any other letters from jobcentre or dwp.
As my situation remains unchanged, nor have i worked or drawing any sort of pension ( I am only 52) I have had my p60u tax details through for year ending April 2017 showing my only money is my esa. I have had no reason to contact them.
I am worried sick that it is either a scam or they are going to tell me I owe them money when nothing has changed??
What am I supposed to do over a telephone interview anyway? I can't show them any of the documents they have listed over a phone ??
I have no query over my pip award, as it's a different criteria to the dla I applied for in 2009 , but this awful letter out of the blue about esa has really upset me.
Help!!

Many thanks Gordan. Having had a chance to look through all my paperwork, I have another number that I will contact them on tomorrow as you have suggested.

I will post what they say once I am sure I am talking to legitimate DWP staff.

Hi Gordan after doing a lot of ringing about this morning, and finally getting a land line phone number to ring, the document sent to me was from the DWP.
The reason it had been flagged was because I volunteered to be a patient partner with my local Rheumatology Hospital.
The hospital is a teaching hospital and I volunteered for patient input for a graduate doing her 3 year PHD. Unfortunately the university involved when they put their paperwork through their systems put me down as a lecturer !! I have never worked for a university only volunteered as a patient through the teaching hospital!!
I only ever received a payment of £100 a year for expenses which the university assured me they had done all the paperwork for.
As I am in the support group and allowed to do permitted work up to 16 hours a week( Not that I can any way), and as this was voluntary (NOT Paid) over 3 years there was no case.
I had not informed the dwp as volunteering ad hoc and not even 16 hours each year let alone a week, I had no need to contact them as this was not paid work over 16 hours.
The telephone interview was cancelled and I was not required to give any financial details that the awful letter stated.
The person I spoke to at DWP ( I have his name and direct land land number) said this often happens and apologised for any distress caused by the standard letter, but they are required to find out the reason.
I shall be contacting the university representative who I volunteered for to advise them, ( to stop any other patient partners having to go through this) that they look again on how they put their paperwork through their systems!!
I volunteered for my local Rheumatology Unit as I wanted to give something back for all the care they given me over the 30 years I have been under their care with my severe chronic Rhuematoid Arthritis. However If I known this was going to happen I may have thought twice!!

Thank you for your all your help over the weekend.