Game charges interest on a 0 balance

I paid the balance of my account on 28 October and was charged interest on 10 November, how does Game charge interest on a 0 balance? I then phoned their customer service number listed on my statement and the lady I spoke to kept telling me that the balance will only reflect at the end of November...she had no clue what I was querying, no matter how many times I tried to explain it. She also told me to hold on while she check with a supervisor and then came back with the same answer. She then told me to send an email, which I did on Friday 17 ********** - they have not yet got back to me or have I received a courtesy response.