Double debit

My bank account was double debited and when I made enquiries no one wanted to assist or send me an invoice specifying why. They then added an additional amount for double debiting my account. Which was never explained and I have been querying it to avail. If you make a mistake you must own up to it and apologise. I don’t know why I am being punished for a mistake you made. They were reluctant to give me a refund and wanted to keep my money as credit without my consent.