vodacom dont keep their promises

I was offered a wifi router contract and was told that if i was not happy with it they would cancel the contract with in seven days. When the router arrived it did not work, i phoned them and asked them to exchange it. The second one also did not work properly so i told them to cancel the contract. This was the beginning of February. I received a credit note and was told the device would be collected shortly. they only collected it on Friday the 10 of March and have charged me for March and now they say i have to wait 7 to 10 days for the contract to be cancelled and another 21 days to get my money back. This was suppose to have been done at the beginning of February. beware they do not seem to do as they say!