Sprint PCS - Sprint I got their phone service through work and 2 days later they cut the service off and sent me a bill over $500 Internet

Back in 2000 a Sprint PCS representative came to my job offering specials on their services for the employees there.  I went in and looked through all the phones they were offering and the package deals they had.  They kept trying to sell me a Nokia flip phone which I told them I didn't want a flip phone just a regular one.  Then I picked out my package which included 1500 minutes a month.  About a week later our phones arrived and when I opened the box it was the flip phone I didn't want.  I didn't feel like going through the hassle of having to trade it out so I accepted what I got.  I went to a payphone and called the toll free number and had the service activated.  I used the phone to call a few people totaling maybe 40 minutes air time and 2 days later my phone is turned off.  I called sprint and asked them what was going on and they said I went over my credit limit of $150 and that my bill at the time was around $450.  I asked her how that was since I just had the phone for 2 days and only used 40 minutes of the 1500 on my plan.  All her response was was that my bill reached over my limit and that I had to pay that to get my services back.  Well I told her I wanted to cancel my services and that I had 30 days to cancel the contract without it being breeched.  So she gave me an address where I can send the equipment to and I did certified so I can run a trace on it so  I know they got it back.  I paid for the first month in advance at my job when they came out so I didn't feel after 2 days of service that I owed them anything, if anything they owed me for the month minus 2 days.  Now I get collection agencies calling me all the time to pay that bill and I refused.  I change my phone number and they still find me.  I even moved 1800 miles away and they still find me.  I have explained to the agencies what was going on and how I don't owe them anything since I didn't get the service as promised and that they got their phone back.  They say I have to talk to Sprint about it which I have done and that I have to pay them and get my money back from Sprint which I wasn't about to do.  If Sprint can't credit my account whats the guarantee they will return my money to me after paying off the agency.  So now I have a bill on my credit report from sprint for over $500 for 2 days services, a phone i didn't ask for and nothing to show for it.