Telkom

Good Day

kindly assist, i am very angry right now, i have a contract with telkom for years now, and i am paying only R299.00 per month, however i was debited R749.00 in December month, for what i dont know, now i recieved an sms to say i am handed over to debt collectors, tried several times to contact Telkom to find out exactly whats happening, however my calls were dropped, please assist as soon as posible thanks