BAD SERVICE

We recently visited Mc Donald's in Brooklyn, Cape Town. We ordered a Club Sandwich and 2 tall cappuccinos. We paid online or should I say at the stations provided instore. Our slip was handed to one of the assisting staff and was told to seat ourselves they will bring the order. More people entered and let left, only to realize we have been waiting 45mins and no one even came to attend to us. We then decided to cancel the order, as when we got to the counter, our no. on our slip never even appeared on there screen. We were declined our refund but a guy on duty who said he was the supervisor. How do we go about resolving this.