Also, you can stop the demanding calls altogether. Just send them a letter in writing asking them to cease communications with you. You are actually asking them to stop sending you letters and to stop calling you. Under the law, the collection company must abide by your request. They can get sued if they don't.
Also, You can sue if they violated the law while contacting you. First off, they are not allowed to contact you at an unreasonable time (after 9pm). If they made these demanding calls at an unreasonable hour, then you can sue them.
Also, these companies are not allowed to threaten you when the make their calls. If they threaten you, then they could get sued. So there are some key restrictions to how these companies can contact you.
You should not feel like you have to sit back and take these demanding phone calls from this company. Especially since you say that you already have taken care of these debts. You should get rid of this nuisance immediately