Misleading & impossible to cancel expired contract

I had a data contract that I had set a 1Gig limit on it for a tablet I bought for my son. All of a sudden that limit is no longer a limit and my son overspent on that account costing me R906.00. Becuase that contract had already expired I therefore decided to cancel it because I do not have control over the spent limit on the account. On 3 occasions I called 084 143 option 2 for cancellation & everytime I call it is the customer care consultants that picks up the call. Two of the consultants I spoke to insisted on putting me through to cancellations department despite me telling them the phone hangs up everytime they do that. It was only when I called the 3rd time that the 3rd consultant told me that the cancellations department is closed till Monday. It now start to look like Cell C deliberately makes it impossible to cancel expired contracts so they keep debiting us unreasonably by using this tactic of increasing spent limit without account holder's consent. This is unfair, misleading and a very irresponsible way of doing business. It should be easy to cancel as much as it is to open a new account and the customer care consultants should be able to asssit in that regard as well.