Hi Pete
If the tenant moved out 'a few weeks ago' then they have forgotten to have the final reading and the power disconnected.
Apart from you using power which will be charged to them, we have had two experiences of similar things happening
We had the power connected - well, we asked for power to be connected - immediately on settlement. This took about a week with numerous phone calls to the supply company, emails and after a lot of messing about the power was connected a week after settlement.
Luckily for us, we weren't moving in, just wanted power for a few jobs, to check appliances etc
We then emailed and phoned to have the power disconnected. The power company didn't disconnect and the tenant didn't have the account changed to her name or connect to a new supplier. We found this out only when we received a bill for nearly $300 about two months later.
We could not get the tenant to provide details of which supply company she had supposedly connected with, so paid the bill and rang and and sent more emails to the supply company
Eventually, when this tenant was evicted about eighteen months later for non-payment of rent the Tribunal awarded us reimbursement, but fat lot of good it did us. She never paid the rent and never paid the electricity account, either.
At my Daughter's property, again supply was transferred and we certainly notified the supply company of a disconnection date, which they didn't do. Again, the incoming tenant never arranged for supply, but this time the bill, for one person in a two bedroom flat, came to nearly $800 for two months electricity.
That was a most unpleasant episode trying to deal with an hysterical and manipulative tenant but eventually after providing a copy of the lease, sworn statements etc we got the supply company to agree that my Daughter was not responsible for the account.
Eventually that tenant, too, was evicted for non-payment of rent.
So do the right thing and do it now. Have the meter read and the supply disconnected immediately. Go and check that the power is off. Contact the previous tenant and reimburse them a pro-rata amount based on the number of days in the billing period and the number of days since they left. There will be an 'average useage' calculation on the bill.
It is a problem when we want to get a few jobs done inbetween tenants, but it is most important to not create or prolong messy situations.
What was a simple task - connect and disconnect electricity supply to the property - became an absolute bun fight which went on for months.
So get it sorted as soon as you can
Cheers
Kristine