Promo Voucher - Unable to be used

I purchased a Defy washing machine on 16 June 2020 from House and Home in Pavilion. The item came with a Omo Auto voucher on behalf of Unilever. I validated the voucher and received an SMS to go into a Checkers/Shoprite store to claim my free detergent. Upon trying to use the promotional message and reference code, it kept giving an error therefore I couldn’t use the voucher to claim my free detergent. I have been trying to contact Unilever with no success as the voucher expires as at 01 August. In this trying economic time, I really would like to be able to receive my free detergent but Unilever customer service is appalling.