Energy prices change all the time. They reflect market supply and demand, and fluctuate as a result. They're also affected when wholesale costs change.
The current Ofgem Energy Price Cap is set every three months, reflecting inflation as well as underlying costs of energy. It caps the unit price of gas and electricity for a typical household with a dual-fuel tariff paying by direct debit. But the amount you pay altogether will still depend on how much energy you use.