R5 COINS FOUND AT THE BOTTOM OF MILKSHAKE GLASS!

My family visited the popular Britannia restaurant on Sun 24 JAN 2016 and upon ordering a Bombay crush we found 2X R5 coins at the bottom of the glass,as shocked as were,we called the manager who was unsympathetic and more in a hurry to find out who made the milkshake,after waiting half an hour,all she could come back and say was THEY SORRY and will just take the milkshake of the bill,she was rather arrogant and couldn't care.We visit often and always get great food and service.She did not seem professional and had no way of controlling an irate customer.If any one has some better way to help and what could have been a better way to handle that situation,i would appreciate your advise.