Late calling for ESA Assessment during UC Migration process

Back in December 2023 I completed a ESA50 to continue my IRESA, since then I have successfully applied for PIP , and awarded the enhanced rate in Daily Living, and Disability. Upon receipt if my PIP decision, I called ESA to inform them of my award and they then added Enhanced disability premium, and severe disability premium to my IRESA.

in the meantime I still heard nothing about my ESA50 form. Given the above I thought perhaps they decided that I did not need an assessment and put me in the support group, but no letter came to this effect. Now over a 15 months later and my having called DWP ESA, because of receiving my ESA to UC Migration, as I wanted to know what group I was in.

I was told the work group? I asked about the ESA50, and was told a manager would call me back
A Manager did call me back but stated I could not back date my ESA claim to December 2023, even though it was their fault and not mine.
He even went as far to say that there were even longer outstanding unprocessed forms than mine, and did not seem the least bothered by his comment, then it dawned on me and I asked if the call was recorded, to which he simply replied NO, Out going calls from the DWP are not recorded, no wonder he wasnt bothered by what he said.

Can someone please confirm that I cannot have my ESA back dated to its December 2023 date, and Could I ask for a delay in moving from ESA to UC Migration, as I have not been correctly assessed as to which ESA group I should be placed in, which I believe should be the Support Group by the way.

Any help would be appreciated
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