ESA AND INTERVIEW TO JCPLUS

I have been on Contribution based ESA since January this year, and was placed into the Support Group in July without any assessment. I spoke to the DWP at that time and they confirmed that I didn't need to send any further medical notes and that I 'wouldn't be bothered' until April 2017. This was a great relief especially as I was in the process of going through being medically retired from work because my health was so poor. I am now very concerned as on Saturday morning I received a letter from the local JCPlus entitled 'Invitation to an Office Interview'. It says they need to see me to discuss the benefit I'm being paid and it's important I attend.I have to take evidence with me like passport, utility bill, bank statement and a completed questionnaire. Can anyone let me know if they've had one of these 'invitations'. Are they mandatory? What also concerns me is that they ask for details of any savings I have. I did ring the DWP who deal with my ESA claim and they said they have not requested this interview and that I do not have to give any details of my finances because my claim is NI based. Also can I take someone with me to this 'interview?'
Thanks for any help.

Thanks for your advice. I rang JCPlus and asked about this 'Interview' and if it was mandatory. The reply was a little hesitant at first but then I was told I did need to attend. I advised I needed a later appointment time to allow someone to accompany me and only then was asked would I have difficulty coming in on my own. When I explained about my disability, I was told JCP have very limited info on their systems about the claimants. The advisor was then most sympathetic and confirmed she would speak to her manager about this and she cancelled the appointment. She did take a few details from me and advised that she would need to contact me again in the future for another appointment. However this would be done over the phone and I would be notified by letter first. Once again thank you. No stress now in the new year.