Delivery of goods and incorrect quotation

We were informed that it would take about 2 weeks for the glasses to arrive. We received a quotation for the glasses and paid the account in full as per the quotation plus the R299 for the sunglasses, Less the amount payable by the medical aid. This was on 30 January 2015. Up to here the service was Very Good. Two weeks later we received a call to collect our glasses. When we arrived on 13 Feb we were informed that there had been a mistake on the quotation and we had to pay more. The sunglasses were also not made yet. However the account was a mess and we requested it to be emailed the invoices and statement in order to claim from medical aid and pay outstanding. We were promised the sunglasses would be sent to be made. Today 23 Feb I receive a call that I still ow them money and they will only send the sunglasses to be made once payment is made. I have to date still not received invoices or statements from them. Therefore having to wait another 2 weeks for something I have already paid for. How can a quote be done and then changed subsequently as it seems the bill just seem to keep growing, not being to be able to provide a statement.