Faulty renault regulator?

Anyone got any ideas. My 53 plate Megane has a fault window reg. Phoned Renault customer service in May (ish) time. told the regs only had 5 year warranty and therefore nothing they could do. I brought a non genuine renault reg and fitted it myself (binned the old one) that is now faulty after 3 months (will be contacting the supplier)
however.....it now appears renault have changed there warranty to 7 years which my car has just fallen into and they will fix it by contributing 75% of the cost. Correct me if i am wrong but i guess renault will tell me I have voided the warranty??? my argument is that there was NO warranty on that part when i chose to replace it myself. Do I have any rights or any leg to stand on with this?