My ex Mrs worked for talk talk in retentions and was able to give insentives to customers to keep them sweet.
Next time you find any charges on your account, contact customer services and kick off, you are not happy with their service and want to know what they are prepared to give you to keep you happy. Initially the answer will be we cant help you sir, so you take the agents name then ask to speak to the duty manager (this is all recorded so they have to comply) you then go through the same routine, complaining re the service, how THEY have allowed a company to charge your account for call's you didn't make and how unsatisfied you are with his/her company and you are sure you would recieve better service with an alternative provider. Take the duty managers name and tell him/her that you wish to leave the company and seek another provider. With talk talk you would then be transfered to retentions, this is where you can bargain with them, basically what are you prepared to do to retain my as a costumer, they may be unable to acctually refund the charges but different tarrifs and wavered monthly charges are a possibility so just stand your ground and see what they are prepared to offer you.
We had a fault with our Virgin internet service when they had a break down in comunication within the company, as an existing customer we were offered a new TV package for £25 (installation cost only) although someone forgot to tell the accounts department (normally £150 + £25) so due to some policy supposedly to prevent customers getting to far in arrears they switched off our phone, internet etc. Big misstake, by the time Marie had finished with them we had £200 credited to our account and the installation free of charge.
Ok so in the Virgin Media case we were in the right, they messed up the service and paid for it, but I've seen my Ex argue with agents when she's been blatantly at fault and still come out on top.
Trouble with us Brits is we're not used to complaining