DO NOT DEAL WITH AGENTS CALLING YOU TO EXTEND CONTRACTS

I get a call from an agent on 2 Feb telling me my contract expires. He sells me a new contract with which I am very happy as the total cost is less. When I get my account at the end of the month I am shocked to see the total amount has increased. The reason is that on 1 Feb the payment for my OLD CONTRACT was invoiced and then on 2 Feb the amount for the NEW CONTRACT was invoiced. This means that the old contract was paid for in full, used 1 day before the agent called, and then cancelled, but already had been paid for. The agent did not mention this at all and I assumed that the new contract would kick in when the old contract was not in operation. My viewpoint is that the agent should either made me aware of the double costing, or made the start date of the new contract 1 March so that there is not double payment. I called customer care 7 March and spoke to Patricia who understood the problem but said it was another department and said she could not help me. I am very unhappy about this as I see as being dishonest and not having the customer's interests at heart.