If you want to to cancel a contract for services made over the phone or online, you have rights under the Consumer Contracts Regulations.
You can use this template letter to help you.
Dear Sir/ Madam
Ref: [Order/Contract number]
I recently entered into a contract [add details] on [date] [over the telephone/ online].
In accordance with my rights under the Consumer Contracts (Information, Cancellation and Additional Charges) Regulations 2013, I would like to cancel the contract.
I require written confirmation from you that the contract has indeed been cancelled and that no payment will be claimed by you.