Tim Hortons review: employee

Went through the drive thru and could see the total for my order on the order confirmation screen was 6.99 for a medium ice cap with choc milk and a no egg no cheese sausage farmers wrap was also told that by the person who took my order however when I got to the window I gave the person there $6 while I counted out the last $1 he then told me I owed $2 when I told him my order was only $6.99 he proceeded to tell me that he wasn't who took my order and I owed him another $2 his name was Martin. I order the same thing almost every time I go I usually get either a large or extra large coffee with it though and it's a little over $9 when I do. Therefore I know for a fact that it was only $7 today because there would be a $2 difference minimum for not having the coffee on the order. I thought Tim hortons was in the customer service business, not upset and be rude and rip people off business?