Extend disconnection date

I’ve been a Virgin Media customer for the past 10 years. Recently, I moved to a new area where Virgin Media’s service isn’t as reliable, so I decided to switch to a different provider. At the time of my move, I was in the 17th month of my usual 18-month contract. I made it clear to Virgin Media that I wanted to keep my existing contract unchanged, as I wasn’t sure how their service would perform in my new location and might consider continuing if things worked out.Everything seemed fine until I requested a disconnection after my 18th month contract . To my shock, I was hit with an 'early disconnection fee' of £1,461, despite the fact that I never signed or agreed to a new contract. After spending countless hours over two weeks explaining the situation, Virgin Media finally acknowledged their error and applied a credit to offset the charge.
Fast forward to today, my new broadband provider can’t install my service until 8th May 2025, so I asked Virgin Media if I could extend my disconnection date to 9th May 2025, just 10 days later than the current schedule. Their response? A flat NO. Worse still, they threatened that if I delay the disconnection, the credit covering the wrongful £1,461 fee would be reversed!
I’m honestly at a loss for words. That charge should never have been applied in the first place, and it feels unjust to be penalised again over such a small and reasonable request. I’m deeply disappointed and frustrated with how Virgin Media has handled this.
If anyone out there has faced a similar situation, I would genuinely appreciate any advice on how to extend the disconnection date by just 10 days without losing the credit that was rightly applied to my account.
Thank you.