Need Advice!

I am in the process of signing the contract for my next assignment, but I am having a few issues. Because Christmas and New Year's fall within the weeks of my contract I requested to know which one I would be required to work or take call. At first the agency told me it was too soon to have all that figured out, but once I got the contract and saw the contract mentions holiday work I asked for it be included into my contract. Then the agency said because I didn't discuss with the nurse manager during my interview what holiday I would be working they could not include it in my contract. So I told them I wasn't going to sign until it is figured out. I am just trying to make personal plans to be home for either Christmas or New Year's, plus I don't want it to not be discussed and then I have to work or take call for both, or don't get to go home. Well the agency has been calling the nurse manager since last Thursday and no response. So, today they gave me her telephone to call and see if I could get the information and still no response! I am starting to have bad feelings about the whole assignment! In my opinion there is nothing worse than a lack of communication. The other thing my contract fails to mention is mileage reimbursement, and the recruiter told me I would still get the reimbursement, but I am signing a short form contract because I am already traveling with the company so it does not need to be mentioned. Since I entered into a verbal contract at the time of the offer am I obligated to take the assignment regardless of the holiday work schedule or do I have the freedom to walk away until I actually sign the contract? Any thoughts? Thanks!