Non payment of credit

This stupid company owes me money and I’ve submitted what they needed which at first was the proof of payment and the next thing I received an sms stating that my case has been resolved. No payment has been made and I called to enquire but was asked to provide the proof of payment again and the very same thing happened but this time when I called I was asked for a bank statement instead of the proof of payment. This has happened more than 3 times. And the case is closed again and I’m being asked to provide a proof of payment again!!! What nonsense is that? The most annoying part is that when they ask me to send the paperwork they ask me to stay on the line to confirm receipt which they and even reply with a case number ***9 to confirm. I’m just going to escalate this because the last time I lost out on a house I wanted to purchase because they had listed me on ICT on a contract that had expired and had been paid with a confirmation of cancellation! This time I’m definitely suing!!!!