They asked me for my IRP5 last year May and told me that there was refund due

They asked me for my IRP5 last year May and told me that there was refund due. I send it and after some days I then called to check if they received the documents. They said yes and that my refund was paid to a person unknown, I then asked for proof of payment so that I can go and open a case because they claim that those bank details were under my profile, they refused and said they were going to investigate the matter I kept calling them but they were never able to assist to date. So today I received a statement showing that I’m now owing them