Billed wrong and food not on standard

I took my children for a sushi/ belt treat at the Cobble walk branch. It was in the afternoon and we were the only customers except for one other table. The food on the belt had obviously been there for a while and they looked like they were preparing for the evening rush. We waited for very long for hot food orders. After enquiring before we went there we were billed wrong which I only realised later at home. It was my daughter's 7th birthday and supposed to be a treat.