Telkom is billing me for a contract that has ended

I was on a 24 months cellular contract with telkom which the last instalment/debit order went off on 1 November. Today is the 1st December and I have been billed AGAIN. After calling them to confirm my cancellation on the 2nd October (a month prior to contract ending) instead of helping me- They cut my network service and I have two major events taking place tomorrow 2 December! How are clients going to get a hold of me.