Poor service!

We had two Sim cards. We cancelled one on the 2 March yet they still tried to bill us for both. Due to insufficient funds they disconnected my Sim card. We were told they would send us the correct billing amount and once paid we will be connected again. They keep giving me the run around whenever I contact them. Saying they've logged an e-mail with the accounts department and they cannot contact them telephonically! After waiting for a week I find this unacceptable!