Western Dental Services review: billing

Ive gotten 2 bills from Western Dental. I did have work done about 4 years ago.. Since I didnt get any bills from them I thought I paid my debt. First letter came in March or April of 2019. Stating I owed about 300. This last letter stated they would give me a 25 percent decrease on the total bill. I dont think I owe anything. In 2016 I did question my bill and said it was fine because I had 2 dental insurances.