Bad customer service

I am very disappointed with the attitude and customer service received today at Sainsburys Medowhall Petrol Station. I usually go to BP but had no choice and go to Sainsburys this morning around 9:50 to put petrol in. The total of the sale came to £30.01 i had no pennies or change on me. Gave the lady at the counter £30 and explained i havent got a penny only £50 note, hoping she can let me off this time but there was no understanding from her side instead she was rude and said give me £50 and i will give you change. Didn't really want to break £50 note for 1 pence. I am the sort of person who usually leaves the change and never takese it, and today taught me a lesson that people won't let you off when you have 1 pence short. There was also a comment made by the same cashier- "Dont come back here if you are not happy", how can people work with public with this sort of attitude. People with no customer service just give a bad reputation to a big name like Sainsburys. I will definitely stick to BP after this