Chinese Holiday Restaurant

I was disappointed at the way we got treated when paying the bill. My family (6 adults and 6 children) went for dinner. My cousin has dietary requirements, they said he cant bring in his own food so my cousin and uncle left.
We told them to give tea so adults only, they gave six tea cups.I found out they charge by the cup and told them to take away 2 cups.
In the receipt, they charged us for 8 cups, not 4. My mum then explained to the lady manager why we only had four cups of tea. SHE LOOKS AT MY MUM AND SAYS "Its alright, i know what Chinese people are like"(indicating that we were lying so we could get away with 4 cups of tea). This was so insulting line towards my mum and she insisted that we pay for 8 cups WHEN THERE WERE ONLY SIX ADULTS AND THE WAITRESS TOOK TWO CUPS AWAY.
Its a disgrace to me knowing that there are people of my race out there being racist to their own race.