Poor Customer services and rules always changing

Yesterday I wanted to buy myself Body Shop products , because I received a birthday voucher as a gift. The staff had the decency to contact their manager and find out if I could use my voucher on the R320 promotion. I wasn't even allowed to use my R50 birthday voucher on the R320 promotion. When did The Body Shop come up with all these rules? Is it even true? If yes, then why does customers not get informed. I would really like feedback as my R50 birthday expires soon.