In some cases you might only become aware of this once you've received a bill from a different company. This can occur in a number of ways, as explained below.
How Slamming Works
* Customer details are forged and sent to an ISP, resulting in an unwanted migration from one provider to another. The forger gains commission for the sale while the customer has a nightmare while trying work out what has happened.
* The customer is called by phone, offered details on a new service and told that they are merely signing/agreeing to be sent more information, but in reality this is taken as approval to switch ISP.
* The customer is called by an individual claiming to represent a specific ISP, when in fact they may represent a different provider. The customer might reach a migration agreement but end up finding their service switched to a completely different ISP from what they were expecting.
* The customer agrees with an ISP representative to move their telephone line service to a new provider, but only learns later that their broadband service has also been moved (or the other way around). Sadly this particular tactic has, until a few years ago, been used by some legitimate providers too (e.g. Tiscali, TalkTalk etc.).
Common sense is the best weapon against slamming, never agree to anything over the phone or sign an agreement unless you've read it first. Ignore calls made to you that claim to come from legitimate sources and that request personal details. Telephone marketing, just like doorstep sales people, is something best avoided. Remember, if a service sounds interesting then it is YOU and ONLY YOU who should initiate contact with the ISP via clear, public and legitimately available contact details.
Under Ofcom's rules you should receive a letter from your old phone/Internet company, and also one from the new provider to inform you of a migration. This is supposed to include a 10 day period in which you can put a stop to the process via either the old or new provider. We would recommend that any customers who get caught up in such a situation should also lodge official complaints with the related ISPs.
Otherwise Ofcom does accept complaints about slamming, although they only tend to act once a large enough group of consumers have lodged similar concerns. Readers should also take note of the new switching process, which was introduced on 20th June 2015.
Ofcom's Slamming/Mis-selling Complaints Form