Wrong. You will have to pay nothing, it is up to them to come and get it.
Don't use the telephone any more.
Stop using the car, (which I expect you already have).
List all the problems along with a timeline.
Send them a recorded delivery letter with the above and head it 'Rejection under the sale of goods act'.
Tell them they have 7 days in which to collect the car and refund you.
If you put the tax on, make sure to take the disc out of the car before they come, but not too soon that you could get done for not displaying.
At the end of the time, if they haven't done the business, come back for help sending them a
letter before action
.
If the car was financed, send copies of all letters to them as well, noting that on the bottom of the letter to the dealer.