paying your part

I guess you're speaking about ER Solutions, a collection agency. As far as I can understand, your creditor has sold off your account to ER Solutions. This collection agency will collect the dues from you. It won't have to give the dues to anyone else. To know more about ER Solutions, check out the given page:
http://www.debtconsolidationcare.com/forums/er-solutions-calling.html

Once a collection agency is assigned by a creditor, it will exhaust it's recovery efforts within 120 days.
So, it's better to set a specific time limit for the agency to either collect it or close the account (to be sold/assigned to another CA). 6 months could be a good time limit beyond which it could be sold or assigned to another CA. So, I guess it ultimately depends on the creditor's agreement with the CA.