Each Saturday, as part of Times Money’s expanded consumer affairs section, we publish your questions and invite other readers to suggest solutions. 

This week Tom Harris  wrote to us. He says: ”My broadband provider offers a free month for referring a friend, which I took advantage of. Later I wasn’t switched back to paying, and have been receiving bills for £0.00 since. More than a year on, I’m nervous that I’ll be liable for back charges. Should I cancel my contract?”