Hello,
I recently purchased a 2016 (registration year) Nissan Pulsar C13 1.2L Petrol DIG-T. I bought this car from a private seller about a month ago and it drove lovely for almost two weeks and it's been nothing but problems ever since.

First time I noticed the issue, I was taking an exit ramp off the M50 in gear 3 at about 45km/h when it wouldn't accelerate smoothly and jerked a bit. I thought nothing of it, then it did it again later on the N4 near Mullingar, Edgeworthstown and Longford. I had it checked 3 days later, just for fault codes and cylinder 3 showed misfires. The jerking kept getting worse and worse until eventually the check engine light would come on for prolonged periods and flash occasionally. I then brought it to a fancy garage where they did a compression test and all 4 cylinders are good but the spark plugs were mismatched, and the wiring loom was split. The wiring loom and connector for cylinder 3 had been tampered with and they were damaged, I assumed this was the root of the issue.

The garage replaced all 4 spark plugs AND all 4 coils with OEM parts and their technician repaired the wiring loom and connector. I got the car back off them today, and it drove fine but only for about 15km before I noticed the same jerking issue mildly occuring again. it's not as bad as the day I took it to the mechanic, but it seems like its been reset to when the issue first started.

I saw a post of some people buying this model and having to have the engine replaced entirely under warranty shortly after 2016 but this car has been in use before I bought it with frequently paid tax and NCT done every 2 years. Has anyone else had this issue, please for the love of god help me. The repairs that have been done weren't cheap and the problem is STILL here. I can't afford to sink more money into this car.

please please please help

Hmm, seems like someone had the issue before and a bodge was carried to rectify the issue (or at least attempt to rectify it).
There is an issue with the timing chains and as far as I can see it was a recall from Nissan.
It does suggest that it occurs on hard acceleration (e.g. from a slip-road) and if the chain is slack it can drift away from the timing point by a small fraction (much like a loose timing belt) which can then throw a code for cam/crank timing and result in what you are experiencing.

I would personally replace the engine oil and look to see what has come out - e.g. metal particles and then replace it with the specified oil which may have not been supplied with previously.

https://www.autodoc.co.uk/car-parts/engine-oil-12094/nissan/pulsar/pulsar-hatchback-c13/107484-1-2-dig-t

If you use a quality oil of the correct specifications (as listed in the link above) and see if that makes any difference to how it runs.
If no real difference is noted then I would advise to get the timing chain replaced which will almost certainly make a difference if it is worn