No way to prevent increase of SPG, so co-payments have to be paid twice

I have a plan with an MSA, SPG and ATB. During my MSA, co-payments, etc go directly off against my MSA, but don't contribute towards the annual threshold, which has the effect of increasing the SPG. So I pay once for the co-payment from my MSA, and then again when trying to get through the SPG. I have discussed this with Discovery, and they say I must ask the medexpress chemist to not put through the co-payments. But I have stood with the chemist, it is not possible, once you submit the claim to Discovery they deduct the full amount, i.e. it is impossible to pay the co-payment by cash. By doing this, Discovery charges you twice for the same thing. Discovery has not been able to provide a solution for this, and continue taking my money twice.