Being chased by Reston's for money owed to Spark, but never used them

mystra

Last week i got a letter from Reston's Solicitors acting on behalf of Azzuro Associates ltd who have apparently bought my outstanding debt balance from Spark Energy, for £300-odd. 
I have never had an energy account with Spark, the nearest I got was when an estate agent tried to force us to use them in a property we were renting - we got it put into the contract that they could not do that, Spark til tried it on anyway (this was back in 2014), but we managed to stop them. We paid our bills to British Gas and after a few months in the place, switched to Ovo for the remainder. On moving everything was paid up with Ovo and correct (2016). I rang Ovo to confirm this, they also were able to tell me the property was with British Gas since 2001 through to the date we switched, and not with Spark during that time. 
After the phone call last week with Restons i chased everything up with Ovo etc as above, also with Spark who have no record of me. 
Reston's then called back to say the matter would be handed back to Azzuro because it was statute barred. They said i would have to ring Azzuro in 2 weeks to sort it out.
Today I have a letter from Restons saying if i don't pay them by 16th it will go to legal action. That is the time i am supposed to be able to contact Azzuro (Reston's said not to contact them sooner as they wont have the case yet)
It all seems like an absolute con, i genuinely cannot owe this money, i never had energy supplied by Spark. I paid my money to British Gas then Ovo. Even if they claimed to have supplied the flat til we switched to Ovo there's no way the bill would be so much (it was summer and it was a small flat). 
I've long since moved out of there, luckily my old housemate knew where to find the old contracts and stuff. 
I'm waiting for a call back from Restons but I'm not hopeful.
Any advice is very welcome - but to be clear - i had no energy supply from Spark so I don't see this as anything less than a scam tbh

[Deleted User]

It won't be a scam. It never is.

At best an admin screw up. If you never had a debt, it'll get sorted.

mystra

got the call back from Reston's - they confirmed the matter is closed as it is statute barred. I've asked them to send confirmation letter. 
I assume that's the bloody end of it, just ridiculous that it's only resolved because of that rather than anyone owning up to the fact that Spark made up an imaginary bill! Fingers crossed that's dealt with, but someone is being shady somewhere!