Renewed contract never signed.

After completion of 1 year contract at an NGO, there was a formal apprisal and I had never recieved a renewed contract for the following year. Only after several follow ups I was mailed a new one with same benefits as earlier. This contract was never signed by me and neither did the HR ask for it. After a month,I quit the organization because I was unhappy with the contract and their pay. The organization asked still asked me to serve the notice period and I did. I am now asking for my relieving letters and the experience letter. The organization has asked me to clear 6 days salary as I had only served 24 days of the notice period. The contract letter stating the notice period was never signed by me. During the clearance or no dues there was no mention of accounts team dues I jad to pay. After 15 days I recieved a mail asking to clear my debts. The organization is refusing to issue the experience letter and the relieving letter if I do not clear the dues. I am right in asking for my papers without clearing the dues as I clearly was unhappy about the new contract and I had not signed it too. If it not necessary to have a signed contract , I am eligable to get the experience letter for the first year I served for the organization?