Domino's Pizza — dominos not accepting valid e voucher

I bought a n evoucher from lil app for dominos. The voucher worth rs. 500/-. Now when i try to apply the evoucher in my online dominos order it was not accepted. Dominos not accepting valid evoucher. They say thet they are facing some technical problem so it could not be accepted. Now the evoucher is expired (Date wise). Then they should refund money. Called their centralized number but no resolution till date, everytime they say the it would be resolved by 48 hours, but there is no himt how will they resolve (I. E will refund the money or the voucher will be accepted). Anyway the voucher is still not allowed to be applied. I demand for refund of rs. My 500/-.