Backdated PIP benefit

Is there anything I can do please I feel the government are robbing disabled people of their rightful benefit by not backdating fully to when PIP was awarded following removal and reinstatement?
I have disabling PTSD, osteoarthritis and fibromyalgia with all the problems associated.
I was awarded PIP in 2013, reassessment 2016, had PIP removed December 2nd 2016, went right up to Upper Tribunal who refused to look at it despite the fact there were several clear errors in law, (paperwork/evidence going missing, it and people promised to be there by the DWP not arriving at court etc, etc).

DWP advised me to put in "a new claim", which I reluctantly did, as I had no choice. This latter claim has now been been granted, at MR stage, (as ATOS, IAS, assessor dotted every box insinuating I can manage everything,) ( All points were removed by DWP, relying on assessors report) so PIP is reinstated but not fully backdated, as they have only gone back to the latter claim, ( November 2017), so I feel I have lost 11 months benefit, fighting for what is right even though they agree there have been points deducted where they should not have been! That together with losing 6 years of state pension, (can't retire now until I'm 66, I'm 62 now).