DSTV Asking Me To Pay for their Mistake

Been on the DSTV Family Package for the past few months now and just got an Invoice from DSTV this month asking me to pay double my usual subscription fee in order to continue the subscription.

When I called in and eventually got to speak to a consultant, they said that a while back they mistakenly invoiced me incorrectly for my DSTV Compact Subscription at the time and that’s why I should pay the additional amount.

I see this as unacceptable; as DSTV has offered me many discounts in the past and to come back now and say that they made a mistake with this is totally unprofessional. Why should I be paying for their mistakes!

I then insisted on cancelling my DSTV completely, and the consultant said that I will have to still pay the amount charged for the incorrect invoicing.

I do not want to cancel my subscription but they are forcing my hand here; they are anyway overpriced and half of the time I am watching ad-breaks; nevertheless is there anyone I can speak to resolve this matter?