Unfairly blacklisted

It was 2013 that I went in to a vodacom shop, I paid my contract in full and also asked the lady at the shop to cancel my contract because I paid it completely. After about 2 months vodacom contacted me saying my account is in arrears, in the meanwhile they have taken money from my account. I struggled to get anyone to answer me after 3 months of trying to get answers and had to email them the proof of payment I made at the vodacom shop, they finally refunded me the amount they took after the payment I made. So today I find out vodacom went and blacklisted me! I would pay someone if I owe them anything but I don't owe vodacom money and to me this is completely unfair to me and my name. Would just be wonderful if vodacom can clear my name.