backdating universal credit claim

Hi, I was diagnosed with bowel cancer and told an operation should remove the tumour and I could well be fine afterwards. I went to hospital for a covid test and then had to isolate till my operation. This means I could not work from 20/05/22. I wasn't going to make a claim for universal credit as my wife works part time and I thought I'd be fine after the op. However, I was told on 01/06/22 that they recommend some further treatment (chemo probably) for approx 6 months and it is likely that I won't be working. I decided to make a claim for universal credit and started it on 01/06/22 but didn't submit it till 09/06/22 as I wasn't very well. At my first appointment I asked if I can backdate my claim to 20/05/22 as that was the date I could not work from. They took the details and said I would here back about it. Today I have had a response saying sorry but no backdating as although I was not able to make the claim any earlier, there is no evidence to show my wife couldn't make the claim for both of us. I started the claim off and my wife only filled in what I asked her to and neither of us thought we would be in this position any earlier. It does say I can ask them to reconsider if they have overlooked something. Has anyone ever done this this or knows of any success with this?

Hi, thanks.

I submitted a fit note for the 20th as the doctor agreed i couldn't work from then. i can't apply for esa as i was self employed and didn't make enough to pay tax etc