Account Still being debited

I requested cancellation of service at the beginning of June as I was relocating I was told to supply the name and number of the new owners otherwise there would be a 3 month cancellation period. I was unaware that this was the case and as I am not a sales person for Chubb I do not think that this is necessary. I requested the original contract from them in August but have not received a reply. I therefor requesting that the payments made by me since July be refunded. What must one do to cancel this service?