I live in Ontario, Canada. Approx. 4 years ago I moved out of a condo in Burlington, ON 1 month early. Supers of the condo at the time managed to find new tenants to the unit so we would not be liable to pay the last month. 4 years later I received a phone call from a company who now owns that same condo claiming I owe them the last month rent & if I do not forward payment, collection agency will be involved. My question is "Do they have the right to demand this payment after 4 years & if so how can I prove that the unit was rented or not rented for that month since this company was not the owners at that time.
I thank whoever answers to this in advance.

Well I'm going to assume you don't have anything in writing from the landlord saying the condo was rented when you left. You could try going to your old condo and see if the same people still live there and if they would sign something saying they moved in and paid rent since the month in question... just a thought

Unfortunately whomever they were moved on & new tenants are there now. Also company is claiming SOL gives them the right to demand payment.

Well it does, but then again why did they wait 4 years, this looks bad on their part if it ever goes to small claims court. Hmm, if you could prove the day you left and (somehow) prove that someone was in that condo the next month then I think your in the clear. But how to prove there was an agreement that the final month rent was not required would be more difficult.

Actually, I think you should pay it rather than fight it. Unless you have documented proof that the supers agreed to waive the last month's rent, you owe for the last month of your lease. The current owners are probably correct that the SOL hasn't expired yet. In addition the fact that they are new owners doesn't shed a question on why the wait. They simply claim that, going through the records after acquiring the property, they found that you owed them. So you are unlikely to win this in court plus you will also lose court costs and your time.