Lack of competent assistance now costs me money

I went to have new spectacles made from Specavers at ********** After seeing the optometrist and finishing the tests I were referred to another lady who compiled an invoice and I asked her : "Is there any co-payments that I have to pay? Is the medical aid covering all?" She rep**** "No, there is no co-payment. The medical aid said there is about R 5 000 and my spectacles only came to about R 3 200". I told her to order and I left. Days after I was sent a message to say I can collect my spectacles. Now, days after having the spectacles, I get an sms stating that I need to pay R958 to them, for coating that is not covered by die medical aid. WHERE MUST I NOW GET THAT MONEY FROM? I asked the lady before ordering the spectacles, otherwise I would have not taken the coating/ other frames. This is ridiculous!!!