Sorry to hear this buddy. Really do feel for you. But this will help:
Looking at your pictures I can confirm your issue is 100% identical to my previous issue.
What's happened is the following:
Water had collected under the car over some time and has been rising as it cant find a way out (design flaw)
The water makes its way out/up from a small gap just under the vent under the driver's seat and pools in the rear footwell. If you stick your finger down there you will feel a deep puddle of water.
If it's not treated the water will eventually end up under the little control module under the driver's seat, and your seat will stop working 😞
I had mine done privately, and the easiest, cheapest and quickest way is to get under the car and remove the carpet/cover from under the car, and you will find some rubber grommets (I think there are approx. 5 of them); one by one pull all of them out and watch the waterfall (have a bucket) – dont bother putting them back in.
This does not fix the issue however, the water will find its way out.
To be on the safe side, I would just probably do both sides while you're at it.
It should take a mechanic around 10 mins to do each side, so it shouldn't cost more than £50
I am not a mechanic, so please do your own research; however, following this method will save you £1000s, and it's an instant fix. Please dont bother wasting any more money on a mechanic diagnosing the issue, not worth it in my opinion.
I hope this helps you out, it's really disappointing knowing after spending all your hard-earned money you're having to deal with unnecessary BS
Keep me posted!!