Charged for no service

On 29/01/2016 I signed a month-to-month contract for fibre internet at Cresta on the understanding I would only be connected when fibre was installed to my home. On 09/02/2016 fibre was installed, but I decided to cancel the contract via email. The following day I received a modem via courier, who refused to return the modem without consent from MWEB. I phoned MWEB who claimed they had no record of my cancellation even though I had a reference number. I took the modem to Cresta, who refused to accept the modem. After waiting an hour for head office to respond I left with the modem. Head office finally phoned back the next day and after several phone calls and numerous false allegations (I had signed a 12 month contract therefore I could not cancel, I had not taken the modem to Cresta, I had cancelled by phone, I had accepted the modem therefore the cancellation was null and void) I was told to take the modem back to Cresta, which I did. Cresta again refused to accept the modem as head office said the modem is my responsibity and they can't take it back. I am now being charged for 2 months of service, which I did not receive, plus a modem which they refuse to take back!!