Suing collection agency, please help

I had an old USBank account that went into collections in 2005, and was closed later that year. I did not find out about the account being negative until a collection agency contacted me in 2007. I told the agency that I needed to know why the account went negative, because I had not taken any money out in quite some time. They could not give me the information, and did not contact me any further.
Then in November 2007 I received a letter from KB Merrill stating that I owed $550 on the account. I called them and told them I disputed the debt, and would like additional information. They did not contact me again for 4-5 months, and again I asked for an account statement. (US Bank said they could not provided me with one because the account had been sold) Again, I heard nothing until September 2008. They asked me if I would be able to pay, and I said I would not until I received an account statement.
2 weeks later I received a message, stating I must call, because the account was going to leave the office. I called, and offered to give them $200 (just to finally put an end to this). They told me that the new balance was $2,200, and that they were a new collection agency. They said that they were going to take me to court and sue for upwards of $5000. I told them that I had a letter from the old company showing the balance to be $550. They told me that The old company sold the account back to US Bank, and Us Bank added the $1600 within the two week period. (Us Bank said that the balance was $400 when it left their office for the final time, and that it was completely sold off.)
I then received 8-10 messages stating "litigation" would be taken against me, so I called them back, each time, I asked them for a letter stating who they were, what the account was for, and what I could do to dispute. They said they didnt send out letters, and that the only way I could get their address was to give them a post dated check. THEY DIDNT EVEN SEND ME AN INITIAL LETTER STATING THAT THEY WERE COLLECTING ON THE ACCOUNT.
So finally I sent them a DV letter. After 40 days they did not get back to me, so I filed a suit in small claims against them. To this day, I have not received any letter from them, or verification of debt. I filed because they Threatened to sue me multiple times, they never sent me a letter within 5 days of initial contact, they increased the amount of the debt from $500 to $2200, and were looking to sue for $5000. I am also suing because they wanted to charge me up front, before they would even tell me what company they were, and where they were located. I have everything on tape, and records of the balance being $500 from the last agency. Do I have a case??