Will I be commited to give them back this 6000+ even if it was not my fault as I think? This money was available on my account and then when I took it changed to unplanned overdraft.

I am after therapy in rehab center, but I had two weeks of reversion in February. Now everything is ok aside from this 6200gbp in Natwest...

Hello, I have a problem with Natwest. I am addicted to gambling, about 2 months ago I gambled a lot in online casino, I made many deposits and withdrawals from 500gbp to even 6500gbp in a short period of time. One time I noticed 6200gbp available on my Natwest account, I was sure that it is one of my withdrawals from casino. I deposited that back to casino and lost it. A few days after, I noticed overdraft of 6200gbp on Natwest and after next few days they closed my online banking. I can't even login to see how much is there now. What should I do? That 6200gbp was available when I used it. Is it my fault?