U Dont Save at this outlet

I have for many years been a loyal customer of Spec Savers - in later years the 4ways branch- whilst they have been more pricey they offered good service and included insurance cover in their fees - recently a leg broke on my glasses - I was quoted R140 to replace them in 5 days this I accepted – offer +acceptance = a valid contract (Commercial law 101) I was then contacted saying that the frames were discounted and I was to choose another – to my surprise they expected me to pay R900!. The customers should not be prejudiced by unavailability of the frame which should have been checked beforehand