bad service

I went to Specsavers brits small and requested to buy the glasses as i have done it before at Specsavers centurion however i was told that they don't support my medical aid and i must pay cash, i asked how possible is that and i was told that Specsavers doesnt support discovery, please assist with resolving this matter because britsmall is the only branch that is close to where i stay and i cannot pay cash because i have medical aid that i pay every month for those services