Your cup size is too small
Second Cup changed their cup sizes for cold beverages a year ago but it seems some franchisees are still using a mix of old and new cups. The result is that they are selling "medium" drinks that are the same size as "small" drinks. In the Toronto Star article it mentions that franchisees are unwilling to throw away old stock because they have to buy the new stock themselves. The article's author suggests Second Cup crack down on franchisees and make them throw away the stock. There's an even simpler solution: since the old "medium" cups are the same size as the new small, just use old mediums as smalls and buy new medium cups. Until then, franchisees who are selling old medium cups and new small cups are ripping off their customers.