Hi, and welcome to the Forum!
Dell have now virtually discontinued the 'old' 10v model, although certain configurations are still available in some countries.
In some cases they are trying to persuade purchasers to accept the 'new' model 10 for the same price, which is not really a lot of help if one of the the first things you want to do is to install OS X.
You don't say whether you are in America, or the U.K... or somewhere else altogether, but the fact that they haven't actually cancelled your order altogether yet is probably a good sign.
If you do call them and again, and mange to speak to a line manager, or supervisor, you should at least be able to get your order expedited!