Cannot process my voucher into my prepaid meter

I purchased a R100 electricity voucher but was unable to load it onto my prepaid meter. immediately after I input the number I get the smiley face and the sad face pop up n the display of the meter.. I have sent an sms and an email to the unipin support center almost 12 hours ago and have not received any feedback so i'm not sure if this support service is even functioning and I only have about 6 units left. My serial number for the voucher is ***