No bueno! First things first, check your meter and see if the number is higher or lower than the bill; occasionally it will be an estimate in which case you should be able to provide your own actual reading to your provider, or it will right itself by the next bill.

Next, if the read is accurate, check for leaks. Generally you will need a plumber to check for you, but better to be safe. (Edit: adding, if there is a leak you will most likely still be liable for the bill).

Otherwise, it may just be the gas price increases have come into effect, and you're seeing that on your bill now.

Source: many years in energy call centres.