If we make a payment and it is received by the time due, can they deny our payment?

We were in the middle of doing a loan modification with our bank, we sent them the proper amount and it arrived there before the due date. It was a trial loan set for three months in the amount of $681.69. We sent $682.00. We received the loan modification letter on Feb 19, 2010; we signed and mailed the letter on Feb. 20, 2010. it stated if we have any questions to contact our lender. we did not have any questions, so therefore we did not feel the need to contact them, however, we were told that we did not comply with the arraingments that we made and our modification loan was cancelled. we received that letter of cancellation on march,saturday 27,2010 along with a check in the amount of $682.00 and to please contact Sean McKee to make other arrangements. we have tried contacting them numerous times to discuss this matter but have got in contact with noone that has been helpful, along with many voicemail machines. Today on tuesday 30,2010 we received a notice of acceleration saying a payment $4049.86 was needed to be paid in full immediately. A foreclosure statement has been sent to an attorney. Our understanding is we have two to three days. please contact us so that we can explain further. We do not have a home phone due to trying to save our home. but you can contact us through a message phone at my e-mail ASAP please at bboopit69@comcast.net. Thank you for your consideration in reading this letter of S.O.S. we greatly appreciate any help that you can provide. can they do this? is this legal?