Dispute over landlord or tenants utility bill

My tenant left an unpaid utility bill, the utility account was never in her name but the partner who always paid the bill until he left her.

She then left about 3 weeks later by informing me but left the key in my post box (I live next door) when I was not at home, so I could not ask/check anything.

2 months later, the new tenants gives me letter addressed to “legal home owner”, which was from a debt recovery company.

I wrote to British Gas who provided the service stating the facts with details of the tenants. I spoke to them and found out that the tenancy was in Julie’s name but the account with British gas was John’s. John had told the British gas that he was leaving, this was about 3 weeks before Julie. I was unaware until I spoke to British gas that Julie was not paying for anything until she finally left 3 weeks later.

British gas told me that John’s account was closed and 3 weeks later, my new tenant’s account was opened, so the time in between was for landlord to pay.

Having given them an account of what happened, British gas has accepted that it is Julie’s responsibility to pay the unpaid bill as she was living during the period in question. However, they have not yet, stopped the debt recovery company from doing anything…. where do I stand in all this?

Thanks

Aga