I've been asked to reply - happy to help...
It's not hard to do but be aware that dealerships will do all they can to stop you rejecting the car so it's mainly a case of sticking to your guns and documenting everything.
In 2017 I took Car Giant to court and won a settlement but it was slow and, at times, a bit of a pain.
The law has changed in your favour since then and Car Giant are a no-frills car supermarket so it's harder to engage with their customer services all of which mean that you should be fine.
The best place for advice is Honest John in the Telegraph:
https://www.honestjohn.co.uk/askhj/answ ... -t-fix-it-
But in a nutshell this is what you need to do:
1. write to the dealership (registered post) explaining that you are rejecting the car and asking that they reply to you in a reasonable time with the process for returning it.
2. explain why you are rejecting the car. If it has been in to the garage to be fixed (for faults, not accident damage) then you should refer to their acceptance of the car for fixing that they acknowledge that there are faults. Explain that the number and repetition of the faults means that you believe that the goods (the car) does not meet the required standard under consumer law
I'd write "Without Prejudice" on the letter at the top and see what they say.
As long as you have notified them that you're rejecting it within six months then that's fine.
Keep us posted but do dig around the Honest John site I linked to above - he is excellent.