Is this Agreement null and void?

On 12/20/08 I signed a contingency agreement to purchase a condo and gave an initial deposit of $1900. Para 4 of the agreement states, "This agreement is expressly conditioned and contingent upon Buyers obtaining a firm commitment for first mortgage within 30 days from the date of this Agreement. Buyers shall apply for such financing with 7 calendar days from the date of this Agreement. If Buyers are unable to obtain a commitment for this financing within the 30 day period, Buyers shall so advise Seller in writing or the contingency shall be waived. If Buyers cannot satisfy this financial contingency, this Agreement shall become null and void and of no further force or effect and Buyers' deposit shall be returned." I provided Seller a prequalification letter for an FHA loan on 12/30/08. Seller then told me only conventional is acceptable. Agreement contains no specification regarding the type of financing to be obtained. I believe I fulfilled the terms of Agreement, as stated, and the Seller has now changed the terms of Agreement. Since the terms have been changed, I don't believe I can be held to the signed Agreement. On 12/31/08 I notified the Seller, in writing, that I do not intend to pursue conventional financing at this time and therefore would not meet the financial contingency as explained to me on 12/30. Seller is pressing for a letter from the lender saying that I cannot qualify for a conventional loan. Not true-I fulfilled the agreement. Now I just want out.