Verizon Bill Issues

I closed my verizon account in Jan 2009, they sent a bill on 9 Feb 2009 stating $101 as balance. this is too high as my balance was only few dollars. Then they told commitment, charged for closed days also and many other unnecessary charges. Than i received another bill on 22 Feb 2009 stating $18 as credit. I got a reminder for $101 in March 2009 and called service rep to find out the real reason behind that, He told everything is taken care and my account closed and there's no amount to be paid from my pocket and verizon has to pay me $18 and Verizon paid this amount in April 2009. My credit was good in May 2009 and it became bas in June 2009 as Verizon reported credit centre that i had defaulted their payment of $101. I really surprised to see this and don't know what to do. How Verizon expects me to pay a dispute huge bill amount? FIrst verizon should be very clean and should have informed me that i have to pay otherwise they will report to credit bureau. They never gave me time to see all this things and suddenly informed credit bureau without any reminders. Now my credit report falls down because of verizon and don't know how to handle this. Kinldy help me to resolve this