I live in a one bedroom flat that only has two rooms and a bathroom. I’m hardly in my house as I visit family most weekends and work full time. However my bill is over £150. How is this possible?

Possibly you are not sending in readings within the timescale, within 2 days of receiving their reminder email, if outwith this period then they will use estimates.
You can manually check your bill by checking the kWh used and work it out providing you have the start and end readings for the period in question.

@StacieCavell Could you provide us with an up to date reading and we can check the latest bill please?