I am not sure if you guys have or anyone had experienced this issue. Today while driving back from home at the entrance of the building after I turn and accelerated the padel got stuck nearly all the way down. Their were kids running cars parked on the right side. I literally slammed the brakes as hard as I can to stop it. Kicked the padel few times to bring it back up right before it hits someone. There was no carpet or anything that could stuck there. Already am trying find a fix for brakes that doesn't work. If anyone have this problem before please guide before it happens again.

 

Since there is no mechanical connection from pedal to anywhere then the defect must be in the pedal assembly so you should replace it, they are not servicable items. Typically pressing the brake pedal cuts the engine to idle at least it did in my XF - never tried it in the XJ - so I'm not sure if your brakes not working is related or not.

I won't go into the merits of accelerating out of a turn with your pedal almost in the carpet with brakes that you say don't work.

Either way if you suspect your pedal is defective and are 100% sure there is no carpet or other obstruction then replace the whole assembly.

 

I had an experience not quite as drastic, but just as alarming since it took control of the speed while I was trying to drive normally, but wasn't able to accelerate with and through traffic at the time.
There are a few buttons on the center console that surround the shifter knob. One of them limits the speed - and I'm not sure of what it does specifically beyond that, since we can't think of a need I or my wife would have to use it.
Then of course there is the cruise control, with functions controlled through the steering wheel buttons. You know if it's a possibility or not, but since we weren't with you, only you know if you may have activated, paused, then resumed by accident - again, only you know if that might have been possible or not at the time.
Your very new-to-you XJ has a lot of little features that you would do well to read-up on and get familiar with to avoid untimely surprises. The best resource for those features is the owner's manual that hopefully is in the glove compartment.
On the other hand, it could be the accelerator pedal assembly which is a replaceable part (and shouldn't be too difficult, other than contorting to get inverted down into the drivers floorboard).


Price and availability are a function of where we are, and while I can't speak for the situation in Dubai or Abu Dhabi, IIRC, you can find anything in the souks.
Over here in the US we have a few good on-line sources, here's one for example with a few reputable brands of aftermarket accelerator pedal assemblies:
2012 JAGUAR XJ 5.0L V8 Accelerator Pedal Position Sensor | RockAuto

But then I also find the genuine Jaguar accelerator pedal assembly (part number C2D20663) from an on-line Jaguar dealership (again, in US) that I use with the price that's below $200 US - in the middle of those aftermarket options.