Clawback fees that are not justified.

I've had an LTE router for about 2 years now. I request a cancellation of service because I've upgraded to Fiber. Now they slap me with a Clawback fee of R250. they say it is the "courier fee for collecting the modem". Firstly, they did not tell me I would be charged, I feel this is bull**** as I have been with them for a long time. Secondly, they just collect the modem, and a monthly later they debit my account, without my permission. if I had've know about the courier fee for delivery I would have organized it to be delivered by alternate means. Or sold the modem for to cover there fees. That being said I demand a refund.