Unnecessary debiting

I paid up my account in full however they still debited an installment when they shouldn't have, I contacted the whatsapp support and they Say it'll be transferred back into my account however it's been a week and counting and no money has been transferred yet nor have they given me any feedback as to what's going on. This service really sucks, you can't be waiting for more than a week to even get a response. Very unprofessional.