Poor after sales service

Twist Menlyn Mall Pretoria. The Salesman showed me the Vega Mini batterie and I bought one. He set it up. I used up my last Twist Cue cartridge. Then started using my new Vega. The two buttons underneath: one works perfectly, the other works but sometimes you have use your finger nail to press it on. Off I went to get it exchanged. The Sales Assistant did the fingernail thing and said it works so they won't exchange it. She spoke to her area manager, same story, as long as it work even if you have to press it in with your finger nail, they won't exchange it. Very poor and disappointing after sales service.