Cancellation of wifi contract

My son ordered a wifi package deal with them. When we got it we tested it and it was slower as our adsl line. we went to Telkom and ask them why is that and they told us that that is the limit in our area.. so he phoned them and also send them an e-mail in the 7 days contract cooling off period. At work he has a problem that employees are not allowed to use their cellphones during working hours. In the e-mail that he send them and also when he called them he stated that he can't be reach during certain times. they told him that they will cancel the contract and the modem will be picked up. Yesterday ,after no futher response from them he called them and asked them what is going on. They told him that he has to pay R1900 for the modem because they don't take it back. They told him that before the R1900 is not payed they will not cancel the contract. This morning they deducted the monthly payment from him. He also told them that he will take the modem to their outlets but they said they dont want it. So what are we to do now?