Fnb ******** me over unknown INT debit balance.

FNB has been charging me a fee of R250 or so for months and it's recorded as Int debit balance. I enquired about this and they telling me that it's for an overdraft I took with them in 2019. I don't remember asking for an overdraft with them. Worse they telling me I've used 20k of this money but I don't know when or how. I asked for a record of my request n they couldn't, they only have an agreement which is not signed by me but stated that it was opened online and accepted online.

I'm furious because I don't remember making this request and they aren't telling me when I used the money or where.

I feel like I'm being ****med by my own bank and they aren't giving me clear answers. I find myself paying monthly fees above R500.