Rental Company back charging me for Hydro. Legal?

If there is a better Toronto sub for this please let me know

September 2016

• Moved in September 1st 2016
• Was given meter number for Toronto Hydro (TH)
• Call to get assigned to that meter, told by TH that the meter was for a commercial unit below me
• TH puts me on a different residential meter in the building (not my unit)
• Contact TH and Rental Group many, many times to try and get this sorted out
• Rental Group tells me to pay for the other unit and will sort it out later
• TH eventually realizes their error and says they'll be in contact with rental group
• TH deletes my account with them to free up that meter for the actual tenant
• I tell Rental Group to let me know when they have a meter for me
• No response for 7 months

April 2017

• I find a new place, apply to assign lease, they agree to terminate my tenancy early (4 months remaining on lease) as I have good rapport with them and found them a suitable tenant to replace me

• They tell me that the Hydro will have to be reconciled as it is stipulated in the lease that I would have to pay for my hydro

• They tell me that just last week they finally got things sorted out with hydro and have the meter information

• They tell me that they can only see a total usage between my unit and the commercial unit (restaurant) below me and will back charge me for hydro costs based on a square footage ratio

Basically, is this legal? I'm scared that they can essentially come up with an arbitrary figure and hold me accountable for it. My unit is small and I was very minimal with my usage because I had no way to track the usage through TH MyTorontoHydro service. I agreed to pay Hydro, but I agreed to pay for what I actually used. Any advice would helpful.

I am totally fine for paying for my usage, but this method of resolution that they want to use seems unfair. Thanks!