So i was reading guide on how to make coins. they say about every 50 swaps should have pokemon. I've used over 500mil not got a single shiny from them. Is my account bugged or did the rarity chance get boosted?

Random Swap chances may say they are 1 in 50, but that doesn't mean that you are guaranteed a pokemon after 50 swaps. I've personally gone spending 100 million without getting a shiny, but keep trying :)

random swap is really wierd rarley does it give me a shiny i spent a bil and never got a shiny so i dony use it anymore.

the most of my shinys are from the random swap so it easy possible to do i do have over 1600 shinys

Sometimes it can go on forever and still have no luck at getting one. Just because the chances are 1/50 doesn't mean you will get on every 50 swaps.