This sucks.
I would contact the police to log the identity theft with them and contact – by calling – your gas provider tell them what happened and asked them to change/ reset your account details. You can tell them you logged the incident with the police, perhaps the police can give you a written report or case number to back you up or give them the name of the officer in charge of your case.
Then can you please read the Digital Stalking Guide from Women’s Aid.
Search for the following file on the homepage of Women’s Aid:
Digital_Stalking_Guide_V2_Nov_2012
and read the following pages:
Appendix D password security tips on page 51
Appendix E creating new accounts on page 54
I’m sorry this happened to you DYImum. Watch out for other possible account thefts in the upcoming weeks, especially your bank accounts logins. Monitor them all closely. Any activities out of the ordinary should alarm you straight away.
Be safe. Sending you hugs 💕