A company sold my debt that I don’t actually owe

I just got the notice today that my debt of 32.79 was sold to a collection agency, but I have proof that insurance paid out the total cost of the medical equipment and they are trying to overcharge me. The equipment online is 60 something and the insurance actually paid a little bit more than that. Now, it’s totally my fault for not telling them to go pound salt sooner and just ignoring it, but is there any way I can get them to stop contacting me over this without paying it? I can afford to pay it if it’ll make them go away but I want to somehow avoid that without getting calls over $30 for the next few years.