SAA Voyager Reward Scheme, NOT so rewarding

I have voyager miles that was due to expire which I exchanged for an upgrade voucher. I travel for work regularly and use SAA on a frequent base as they do have pretty comfortable flights. When I wanted to use the voucher I then get told my work had to purchase a more expensive version of the "economy ticket" to use the voucher. Surely "Economy class" is "Economy class" and if you offer me a rewards system to belong, you cannot want to charge me additional costs to use these benefits (very contradictory). Perhaps something you need to relook at for your loyal and regular customers as the additional costs for the "same" seat and no true benefit does not warrant the extra/additional costs.