Unfair billing on DStv price lock.

I have a problem with multichoice DStv, Apparently I bought my explora decoder on price lock which is R499, and I have been constantly paying my installments on time, now I'm being told I oncurred arrears on the account and they've closed the channels.

I've tried calling them but no one seems to be hearing me, no 1 is seems to be helping, they insist I pay extra R396 on top of the payment I already made on the 29th of January.

Regards Mosawenkosi.