I may be wrong as I am not Customer Service, (just someone who wants to try to help) but as I have come to know, collect calls do not work with pre-paid services. However,,,,
A great way around this is to utilize a service such as http://www.gtl.net/ or https://www.paytel.com but this changes for every state and I am only making a generalization example , I don' tknow your situation or what state you are in, but there are options, ALSo food for thought, I have also heard of people setting up Google Voice Numbers and using Virtual Forwarding, but I have no idea how that would work because collect calls require payment..
Eddie Starr is right about how non contract services don't include the ability to receive collect calls. Virgin Mobile is a No-Contract service that charges you for your cellular airtime - we do not provide a service to assess and bill you for additional fees and charges generated from collect calls. We hope this information helps.