UC MR for backpayment

i submitted a request in february this year asking for backpayment for my bedroom allowance going back about 10 months (as i wasn't informed or advised i was able to claim for an additional bedroom for a carer until february, i didn't even know i was entitled to such a thing) they awarded me the extra bedroom allowance since february but when i asked for the backpayment they came back within 1 day on my journal and said no, but i could have a MR if i wasn't happy. so i asked for an MR straight away and i have been waiting ever since, it's going on since march. they said there is no timescale?! but this seems ridiculous, how can they make a decision within ONE DAY of if i am to receive back pay but the wait for the MR is immeasurable.

any advice on how to approach this or see when a resolution will be made, i am getting extremely stressed and anxious because i also have a tribunal for my PIP review running along side this and it is making my mental state alot worse :(