Phone call from DM about PIP Review

Hello,
As you see from my updates, my mum was send an AR1 form Feb 17 after filling in and sending back we got a decision on April 2017 of same PIP rates until 2023.
Today we received a letter from ATOS asking my mum to attend a PIP consultation and i'm not sure why this has been send when my mum has already had her decision.
Could you please advise in what we should do in such situation?

Hello,
I rang the DWP office and they have said that there is a note on the system that the file needs to be send to ATOS. The date on the system is 6 days after the original decision letter i.e Decision letter 12th April 2017, note on system 18 April 2017. They couldn't tell me why this is and advised us to go for the f2f.
I suppose the original telephone call from the DM on 12th April 2017 telling us that my mum may be called for a f2f is clear now.
Could you think of any reason why this has happened?

Hi Gordon,

I took your advise and escalated this to a manager who came on straight away. I explained that i had already had a decision two months before for 7 years. She wasn't having any of it and told me that DWP occasionally do this to make sure that the decision is right and there is no time limit on reassessing. After many minutes of arguing i eventually gave up and took my mum to the assessment last Thursday.
I think it went well and took additional reports. We were only in the room for 20 minutes and i felt we were being rushed. Our appointment was at 2pm and we were seen at 2.40pm. She had someone else to see at 3pm.
I will let you know the outcome.
Thanks for your help so far.