I'm so sad for you Nataliea but can perfectly understand MT's point of view. There is such pressure for space among all the rescues and if there are several offers of good homes, MT was bound to take the one that would free up space to allow another dog to be helped. The same thing happened when I wanted to rehome Millie (who came, named Trinket, from MT). Simon was actually away in the States when I spotted her.
I wanted Sylvia at MT to hang on for a few days so I could discuss it with him and let him recover after the trip. I even offered to pay boarding fees. When, however, she explained the situation we drove all the way from Cumbria to Wales the same day he got off the redeye.
But we both work from home so it was much easier for us. You made the right decision for your circumstances - giving yourself time and space to introduce the new member of the family is so important and you were putting the dog first. Happenstance was just against you but there is a cocker out there somewhere waiting for you soon.