The dentist

So this year I started seeing a dentist that I liked very much.  He seemed nice and knowledgeable about his subject area.  I have had bad dentists in the past so I really appreciated someone who knew what he was doing.  So here comes the bad part, I went to have a crown placed a few weeks ago, but it turns out that he needs my other two teeth extracted first due to all the swelling in the gum, etc.  So he removes the temporary crown and does a buildup in preparation for the crown.  I pay, a total of $99, for the work and get my receipt which shows a $0 balance.  One week later I get a bill in the mail from the dentist for $87, it shows a charge of $170 for a buildup and $21 for an xray.  I check my receipt given the day of the service and it showed a $21 charge for an xray and $83 for the buildup.  I received an approximate 5% full payment discount. Obviously, the statement in the mail is a mistake on their behalf I call the office and explain the discrepancy.  I scan and email my receipt to the office.  The office assistant replies, that they made an error on the date of service and they will give me extra time to pay. I was irritated because to me the statement appeared duplicitous. The $83 charge is not listed anywhere on the bill in the mail, I would assume they would have credited the account to show the mistake and keep proper records.  I was furious because they knew they made a mistake, and knew that the statement would be at odds with the documentation that they already provided to me, yet they did nothing to explain the mistake until I called.  Why did I have to waste my time and reach out to them?  Why didn't they note on the bill that an error had been made? I felt that the customer service I received was less than stellar and I will not be returning to the office.  I think it was just one of those things were it hit me the wrong way on the wrong day and I took greater offense than necessary.  Nevertheless, I am petty and will not be returning. Thank goodness there are tons of dental offices in the area.