PIP MR Question

Hi, after being transitioned over to PiP after 20 years on DLA, I lost out on daily living award by 3 points. I submitted a MR immediately after receiving the decision.
I was informed it could take up to 10 weeks for a decision to be made. It has now been 13 weeks with no response/decision.
I called PIP and was told after much humming and Haaaing, that my file has been sent back to the assessment provider. (Independent Assessment Service). I asked if that was usual procedure and was told that upon receiving my 'new evidence' (ie Mandatory recon.) they had sent my file back to IAS to see if they would change their decision.

I was of the understanding that the AP only made the report and that it was ultimately the DWP who made the decision whether or not a claimant wouldI' be awarded PIP. The person I spoke to said 'We must give the AP time to review the new evidence'. Obviously, after 13 weeks, I feel they have had plenty of time; especially if they have to then return my case file to DWP for them to have a 'hard copy'.
In the meantime, I'm struggling on a massively reduced income, as Ive lost my severe disability component of ESA, in addition to getting less than I did on DLA.
Does anybody know if this is standard protocol and if there is anything I can do to expedite the situation as I cannot submit an appeal to tribunal until I get a decision on my MR. I'm hoping that due to the length of time they are taking, it might be a positive outcome, Any advice or info would be appreciated. Thanks in advance Cat