Well, a series of things happened. We actually had it resolved before we heard back from our attorney (which was 2-3 weeks, but we emailed her so that takes longer).
On the day that my husband got the call from the CA (this was on a Friday), he called the drs office - that is when he got the rude lady that said she didn't care who signed - it was his responsibility. She eventually said that she would change it and put it in the mothers name. (I doubted that she was telling the truth the whole time, but we had to wait and see).
About a week later, he recieved yet another call from the CA. He called the drs office back & got the answering machine. He left a looonnggg winded vm about how what they were doing was illegal, he hadn't signed for any bills, etc. They called him back later that afternoon and profusely apologized and said they would put the bill in the mother's name.
This very same day, he received in the mail the bill from the CA. It said "please pay xxx or dispute this bill" etc. I didn't know that he had spoken to the drs office that day, so I was in the process of typing up the dispute info and getting our "proof" ready to mail to them. He called to say that he had spoken to the drs office, but I sent out the dispute letter anyway.. I said in the letter that the name had been changed at the drs office and demanded that they take all traces of this off the CR.
A few more days went by and the CA called again. He called the drs office back and told them that he was still being harrassed and asked them to let the CA know that he was not responsible for this bill. They agreed and apparently contacted them because it is no longer on his CR.
This past Friday, the attorney called my husband. Told him that it was illegal for the drs office to do this and also told him that he was not responsible for any part of this bill since the time frame for her to submit them to him had lapsed. There wasn't much more that he needed her for so the call was short.
Maybe you should contact the dentist office directly and threaten them with an attorney. Dispute the charge with them instead of the CA. When its cleared up at the dentist office, then you can clear it up with the CA.
I got another "opinion" from a legal source re: this situation before it was resolved. They suggested that he request a copy of all documents from the drs office. Go (in person) and ask to see ANY paperwork that he signed authorizing responsibility for those treatments. If the ex wife forged his name - press charges. She also suggested that he get a credit monitoring service (which we did) and submit a "solen identity" statement and put it on file.
Hope this helps you!