Angry macdonalds staff attitude pathetic

I went through ladysmith mcdonalds drive thru , using my mcdonalds app i checked my offers and ordered a happy meal but the 2nd cashier where you pay the attitude is pathetic! Firstly she didnt pay heed to me mentioning the promotion and price to which i was supposed to pay. She then goes on to say the promotions are dealt with inside and she doesnt know anything of it. I had to park the car and still walk inside and explain the situation as i paid more then the offer provided. I explained it 3 times to the manager only for him to have an attitude and make me wait for my money! Mcdonalds need to train their staff as to how to handle promotions and how to be polite! Very upset with this bad service !