Walka Deactivation

I emailed a change of ownership form through on Friday - reply ref [#***]. In this email I specifically requested that the old Walka (SPH******) be disconnected as I didn't want any additional charges to my account and the new Walka (SGH******) be activated only. The change of ownership has taken place, the new Walka is active, but so is the old one!!! I have now phoned three times and they tell my they 'can't deactivate it'. I do not want to pay for any additional services and now because DSTV can't deactivate one of their mobile devices, I will be penalised. It is unacceptable. Please advise asap.