Unfair bill

This is the third time now complaining about this **** called Rain, I wanted them to come collect their router, the said to me I need to pay R1154.00 in order for me to can do the cancellation, and I asked why that amount they said they are charging for services used and or active sim card. Then I removed the sim from the device and try to pay what they said its due to me, then boom it went up to R1749.00. when I sent them a message even now there was no respond. because really I don't understand why are busy billing me for something I'm not using.