Billed on cancelled Contract

I had a cellphone contract which was cancelled in Feb and today the 22/06/2015 i receive an invoice notifying me i have an outstanding amount of R178.59 and an sms which i wish to know for which month is this amount for and for what services is this. When i call to get clarification on *** i got transferred to 3 different agents telling me they can't help since it a prepared services and i cannot be assisted since there is no information on my account.