Settled the account but still in dept

I don't know if I should say vodacom is a **** or what. I had a cellphone contract with vodacom since 2019 November so this year I decided to settle the amount in September because I was on maternity leave and I had no means of income. I paid the full settlement amount of which it was R688.51 and I filled the premature cancellation quotation and submitted as require, I don't understand why I am now getting calls from debt collectors I don't know what am I owing to vodacom because I paid them, this is annoying because I can't even get through to their call centre department I've been trying to call since last month I can't get help about this and my name is now on bad books if there's anyone to assist me with this please help I have all the proof that I paid vodacom in full and all the sent emails can prove. I really need assistance regarding this matter I can't settle the account and still be in debt with vodacom my name is being dragged in mud I regret taking a contract with vodacom.