Hidden costs in contract. Struggling to cancel contract.

Desperately trying to cancel this contract. Was under the impression that the deposit and 24 month payments was all that needs to be paid. Now on examining the paperwork, it states that I need to pay a "reliance fee" for 120 months (10 years!!!) which increases at a minimum of 8% per annum, or the average annual CPI, whichever is higher. The salesman was not forthcoming with this information. I have sent an email to two email addresses and called to cancel the contract, but was informed that my contract is still "in transit" and can only enquire once I receive a welcome email.