Did you not get your Demo Account disabled every 2 months while you were inactive on Live?
If you had put some money on your Live Account, even £100, then above would have happened. Also you would have been charged £30 per month off your Live funds.
The way forward would be to contact the vendor of the System you bought of MarketPlace, explain what happened and provide evidence (email from IG?). I feel sure the vendor will then provide you with a replacement License somehow or other?