Fnb connect

I bought a device with them 4 years ago and it is paid up but they keep on telling me I owe them R1250 when I ask for a breakdown no one gets back to me. I emailed collections and customer services last yesterday August till date no one has responded to my email the last correspondence was I don’t owe anything they will fix the error on their side till today nothing has been done and this is affecting my credit score. I spoke to Didimalang Rakobane and I’ve been sending her emails as well to follow she has since been ignoring my emails as well.