Selling invalid vouchers

I booked a ticket with CemAir to Johannesburg for an international flight. As part of my booking with CemAir I booked and paid for a voucher for access to the 'International Bidvest lounge' as I was going to be on the airport for a few hours. On arrival at the International Bidvest lounge the reception desk did not allow me in with the voucher which I printed. They said that the CemAir voucher cannot be used at the International lounge. They tried to lookup all options but the voucher number could not be used for access. I was forced to pay again for access to the lounge. This time R475. I have reached out to CemAIr about this and their only response was: "lounge access is a non-refundable purchase and we will not be able to offer a refund for this." So essentially , they sell you invalid vouchers and when you complain about this , they just say sorry , it is your problem. Warning to all people booking with CemAir , never buy any optional/additional vouchers from them. As for me and my friends , we will never fly with them again. Stay well clear of this lot.