Western Dental Western Dental sent a bill for "installment payment" it's been 2 years since I'v been there and all work was covered by my insurance Orange, California

It's been almost 2 years since myself or my family has used Western Dental and the reason why we left was the work they did on my teeth and my daughters and my wife. That part is a very long story! since then I have found another dentist, but currently I work for a company that has Dental insurance and during our visits all the services were covered. and yesterday 6/04/012 we received a invoice with account number 192-000664 stating that we need to make a "Scheduled installment Payment" of $148.00 due by 6/17/2012. after being on the phone for over a half hour talking to 3 different people they finally gave use a number of 800-326-3254 and while talking to this individual on the same day 6/5/2012 at 9:54 am when the account number was given my name was attached to it. The representative that talked to my wife stated that he needed to talk to the office that generated the bill and they would get back to us. So my wife asked for the phone number of the office that generated the bill 209-832-0219 which was the local Manteca office that I used to use so I contacted them and they said it was probably a balance found when my insurance company changed form one company to another. I let them know that my company never changed there insurance provider since I have been there of December of 2007. I am posting this due to it looks like a company scam that I feel that has been sent to others not knowing what they are being billed for. So just beware. It looks as though there billing is similar to there services.