Unipin no response and no electricity!

I have bought 3 Unipin vouchers and non of them work, I keep getting a reply that it cannot identify the supplier but I have been loading vouchers from these shops for years on the exact same meter! I have sent numerous sms's and emails with no response to any! I have phoned numerous call centres and no one can help! I'm lucky if I have 20mins of electricity left! This is the most pathetic service I have ever received.