leasing of vesicle

4 years ago I lease a Randavoah van from GMAC when the term was expired I took the van back in good condition, and was told by the dealer that the van was return and check out and was in good standard about 6 month the company send me a letter for $500.00 dollars and because I was unable to pay the money because of a lack of employment . The company turn me over to collecting agency ans I am complaying about the arrastment 3-4 time a day even at night by these people.  I am afraid to answer the phone because of the treats and name calling by these collecting agency