Being called by a law firm with an unknown number

At 16:45 I received a call from an unknown number . Saying I am handed over because of my outstanding balance on my std bank gold cheque acc. I never owned a gold cheque acc. I had a titanium account. I closed my account down last year . They say I owe over 1000 rand and they will call me back at 8 am tomorrow. I want proof of this from standard bank because I even paid to close my account down. This is ridiculous and I refuse to pay for any negligence on any part. I paid for my account to be closed down and I will not pay fees I have no say in. I want standard bank to contact me as soon as this message is seen and to deal with this situation . This is very unprofessional. When I asked why has standard bank not contacted me they say they don't know. They only had my email address . The account number was also not what I remembered I had. If this is a ********** call I want it sorted out and I want standard bank to please confirm this with me. I will not pay a cent for an account I paid to close down in the bank itself!