Incorrect billing

I cancelled my membership with ADT on the 31/12/2018. They have not renewed the radio network of R310 and now they have added it to the invoice.How do they expect me to pay for the radio i never used. Adt needs to sort this out as i was told initially when i cancel by adewcharan that i will not be charged the radio,I have made phone calls where this was confirmed.terrible service!