If you are trying to cut at grade then a band saw.

If you want to yank it out buy a pull jack and get a post puller. Attack pull jack to post puller and crank. It’ll come out.

If the footer is deep or adhered to concrete sidewalk etc you may have to jack hammer it.

Also you can attach it to a truck hitch with a chain and pull.

I worked in the fence industry for a few years mostly doing repairs. We’ve pulled up 6” steel posts with 300 lbs slugs with a pullback and a post puller before.