Misleading Customers

I received an sms from Nedbank stating that I received a R100 voucher from shoprite or nandos valid for 7 days. I responded and nothing happened. I called customer care and spoke to Ayanda, she told me I will receive it in 7 w/days. Still nothing. No follow up and wrong info given by her. the offer on the sms shows it is valid for 7 days and not the voucher. how am I supposed to trust my bank?