PLEASE HELP.. Ovefpaid universal credit

Hello..
I have been overpaid nearly £3,000 universal credit for rent in May.. It was paid to me by my council on the direction of universal credit even though i migrated from esa & housing benefit in november 2025.. I have been told by the council that it will have to be paid back to universal credit in instalments.. I am absolutely begging them to let me pay it back in one go but no answer yet.. I am feeling more desperate than I can say.. I am 64 & have never ever been in debt.. This could take 6 years to pay even if they don't make any more mistakes.. I now appear to have £5,000 in savings but £3,000 is not mine.. It is so cruel & i really cannot cope.. Do you know of any clause or way that they can let me pay it all back in one go as it has only been in my bank account since the 22nd May.. I am clinging on to the hope that i can pay it all back because otherwise i will never be able to understand my payments again & find it impossible not to go over £6,000.. I am so unwell & instead of concentrating on my hospital appointments etc i am not eating or sleeping because of this.. i am totally overwhemed & not even writing this properly because i am just reaching out for advice.. I am already trying to pay back a £200 overpayment in april.. One cheque & this distress can be sorted.. how can they force me to take 6 years at 15% per month?! There has to be some other way.. I have stated that i am very vulnerable & totally overwhelmed but the fact they don't care is pushing me into not functioning at all.. sorry to sound so bad but i cannot face a future of debt that i can pay now but possibly not in the future & also how can they class it as savings when it is not mine..
Best wishes to all & hoping for a solution please..