Formal complaint against cornubia checker

Very bad services.They gave me a voucher for no stock of a product they didn't get stock so the voucher expired was not aware until I call them they didn't advise me that the voucher is valid for 3 months only so I pick up covid was unable to go into the store now they saying I can't use the voucher anymore when I asked the cashier they advise me that I can use the voucher whenever they have stock they didn't even give me another voucher since they had no stock very bad services .