***** on bank account

I had a month to month contract with Supersonic for R399, for more than 2 years, when I contacted them to cancel the service they said I must give one months notice ( so July was my notice month) they said they will send a courier to collect the router at the end of July, no one came to collect it. Today 26 Aug they debited R2500 from my account , when I contacred them they said its for the router . According to me this is ***** , I never gave auth for them to debit any amount more than R399 for the wifi service, and they did not notify me that they will debit R2500 from my account if they dont collect the router from me .