This type of thing happens all to often i'm afraid.
You've paid in full so now, and they only know to well that they can give you a c0ck and bull story.
Someone has messed up along the line and its the consumer that tends to suffer, they have offered you an alternative cooker which they probably knew you would turn down, therefore its on order ''we do apologise'' and will endeavour to get it there ASAP.
Speak to a manager and insist that you want the said items sent to you as a matter of urgency as you have a dinner party planned whiched cannot be cancelled, otherwise you are prepared to write to trading standards and watchdog about there shabby service.
In other words, take charge of the conversation and don't take NO for an answer, mention the amount of time and money its cost you to chase up there error as well