Aspen Dental

I received a notice from a collection agency regarding a bill from Aspen Dental on March 1, 2021. First off this is the first time I have been notified at all that I owe any type of money. I have never received a bill from Aspen Dental and now 2 years letter I find out that I have been sent to a collection agency. I have always paid my balance prior to leaving the office so I was shocked when I received this notice. I went into Aspen Dental in Santa Fe, NM and they couldn't give me any type of information. They said it was an issue with corporate. I have attached a bill from the collection agency. I would like to know why I was never sent a bill. I would also like a copy of the bill to see if this amount is even owed, I would like this removed from collections and off my credit report.