Starbucks

I am a big fan of starbucks. I am honestly visiting the one in near my house everyday.
Yesterday, I was visiting the glen one after dinner with my family.. I ordered cold beverage for myself and kids drink for my son. I ordered cold milk for kid size. And the lady filled up just a half of cup that left in the milk container. And she just throw the empty milk container on the floor right infront of me. And she gave me only half of the cup of milk. I said “can you fill full?” and she said very mean with mad face “you want whole cup?” and she opened another milk container and filled. What was that mean?
I paid full but have just a half cup because milk container empty and she doesn’t want open for another container? With bad attitude? I was frustraing and felt very upset. And right after she treated next customer with smile. I felt discrimination too. The glen one is very crowded and walked a lot of time for shopping and stop by for the drink. This is crazy and uncomfortable feeling that I never felt since I visit the starbucks. I was so angry that I could hardly command my temper.