BAD SERVICE ON DECEASED ESTATE

My father passed on early last year, so after that we received a letter from Nedbank saying there's a refund on the bond that they have to give back and we should submit some document so that the money can be refunded into my mother's account. It's been over a year now and we've sent them documents over and over again but each time they would give us a story on what's missing. Nedbank's communication with us is very bad on the matter, I call to do follow up week after week without getting anywhere with it. This is really upsetting and frustrating.