Cell C credibility

Cell C is terrible with its dealings, I called them and explained several times about the agreement we had regarding contract phone, it was an agreement of R260 of amount to be deducted at the end of the month, but some how they tend to stupidly ignore that. For the past 4/3 months they set the debit at 15 of every month by doing so I pay interest because of the late payment; which is R318 of which that is totally absurd and unprofessional, because on the other side they are ruining my profile.