I need a new chiropractor

Today I received a billing for a service done 4 months ago. I thought I paid my full bill at the time I wrote my check at the office. The secretary told me there was an outstanding credit on my account, so I didn't owe as much. No, I was just charged half and now I am told to pay the other half, including interest for being late. Huh? According to the bill that includes services and payments from 4 years ago, there are lines for insurance. I take it that means they are so accustomed to people having insurance that they do not know how to handle someone without it. Unless they tried to charge the insurance company on my records 4 years ago and were refused payment because I cancelled it 4 years ago. Sometimes I just I hate people. Post later. Bye!