There are a couple of things to do to find a solution.
If you have a prepayment meter, check that there's credit on your account. This is usually displayed on the screen.
Otherwise, heating and hot water problems are usually because of a problem with your boiler, which your letting agent or landlord will be able to help with.
If no gas appliances are working (e.g. a gas cooker) there may be a problem with your gas supply. In this case get in touch with our Customer Support team, who'll contact your supplier for you.