Paying for upsize but got what's not asked for !!!!!!!

On the 18th of April my collage and i went to Mc Donald's Montague Gardens drive thru , we ordered our things as we got to the window to pay we asked the casher to upsize our meals she then gave us a whole attatude and said she can not do it we suppose to upsize it when we ordered , i then asked her to call the Manager that she also was unsure about doing the Manager eventually came just did what she needed to and left , by then we waited so long i just took our food and left when i got back to office i ws charged for a Large Fries but got a regular , i paid for a upsize but got what i didnt ask for

I emailed them i even called them , no one got back to me this is so bad and how many others do they trick on paying for upsized but doesnt get it .!!!!!!