Mtn refusing to have WiFi router cancelled

Mtn is refusing to have my contract tht expired in Jan to be cancelled instead they keep on adding money .When I asked them to cancel it they refused sighting that I must add money ..I paid money but they said it's short cause the instalment I was paying was for 24 months and that special doesn't apply anymore and this was without me knowing.i couldn't cancel December cause of their network problems 😭...Another thing is that I took a contract on 14 th of December and January the 7 the I was told to pay pro rata and something that was never indicated to me in store ..I feel sick with this company I m taking them to the ombudsman