yeah without pictures its hard to say, but you've pretty much have done everything wrong. and Because you tried leveling sagging areas, things will only get worse.

joists have maximum spans depending on species, grade, thickness and width. they also different allowable levels of sag, and periods of time where excessive loads can cause deflection/sag.

also, without blocking, joists/ beams will twist. because a joist/beam is in compression AND tension on the outer edges of the horizontal member, those members get their strength from the height [up and down] and stability from the width/ flange. a joist essentially wants to twist when put under load, to the point its flat, especially in the center. the flatter it gets obviously the weaker the member is. this is exceptionally troublesome in big beams. as you lose upright positioning you sag more as you lose "strength".

wooden joists have no flange, they're usually just 1.5" to 2" depending on age. to fight this twisting, you need lateral support. members acting on members. this is where blocking comes into play. you've seen two pieces Xed between joists, or solid, and sometimes two 1x or 2x boards at top and bottom. if you don't have hangers at joist ends, blocking will significantly help whether it's a wood joist or steel beam. usually blocking is only required on something like 16?ft spans or so? for 2x12s or larger? but what blocking does is help distribute the load, add stiffness by preventing deflection which decreases sag.

this next part depends on span. so what you can do is jack up the floor and sister joist members with same size or LARGER members if you can take the height difference. every 2 inches you add to board height essentially doubles the load they can hold, every board you sister is slightly less. wood quantity for wood quantity, moving to the next 2x size is significantly more efficient/ cheaper and stronger with less deflection. you can notch the ends of the joists to fit a bigger member. while not ideal, it will still greatly benefit. you can also add end blocking on top of that and run joist hangers to support the bottom addition.

you can also add a beam, steel, wood, engineered lumber, again depends on load/span. you'll still likely be sistering the existing joists as they'll likely be permanently deformed. the beam can usually be mounted flush, and joists hangered, but you can also run beam beneath. there's some decent math to do here and no one here has enough information and really shouldn't Because of safety and insurance.

your floor may be within spec and the sag is okay, without pics, or measurements etc its hard to say.

but yeah you made your job a bit harder as once you jack up your floor, your previous adjustments will be very proud. and you can shave the floor if it's a wood product, you likely only have a 1/4 or so before you get down to the tongue. I forget what floor you said you're trying to save. it might look like shit when this is all said and done and you'll be doing more work and money in the end.

if you try something like shimming the floor from underneath, trying to fasten underneath. lol. hope I get to see that thread too. the half assed leveler is likely going to be the problem and was improper assessment. depending how it was discussed, you hired a flooring guy to install floor. it's like going to a boob surgeon and complaining you walked out with big boobies. they work with a lot of out if Level garbage and a lot of people don't do the work to level because they don't care and are likely going to flip it. next time try to assess the issues properly and come up with a plan. you can start now. at least you know who to point your fingers at when you complain about pulling certain things out [yourself]

you may find you had beams or supports and someone removed them. this is the case with a lot of houses because of open concept flipping. you can stay open concept but you have to do it right