FNB no App no service

I settled and closed my credit card account with Fnb and today I get a statement saying there's an outstanding balance owing. I called the help desk and they cannot assist if you don't have their App. I asked to speak to a manager and apparently managers don't take calls, I need to go to a branch to get help. What an inconvenience and such pathetic service. I have a reference number for closure but no one can help. FNB your service really sucks no one takes accountability and you have all the excuses not to resolve clients issues. I need my account closed reference number CAS-***-J8X0S4, if not I will escalate this to the Ombudsman.