I think UPG is UPG - it’s not a great idea to hang your own practice of the comments of ONE person - this is not verified and should be taken with a large pinch of salt. Nothing of what he says is really important, he could be interpreting something else and not know.
since I gave them my blood
You didn’t though? You were intending to offer blood for a real entity, not parasites. They just hijacked the line. No pact is made, no promises given, they are stealing. So it sound like you probably did attract some freeloading timewater, and gave it energy, but that’s it.
Try to stop putting emotional weight to this persons fears, as you will make it true. They couldn’t deal with it themselves, so thier skill level is just not there to be trusting them on this right now.
What is important is that YOU feel blocked. That is a personal and verifiable symptom you can rely on. I think you’re not, actually because I se signs here that you are basically doing magick against yourself via fear, and that is working.
Well you did say
It’s pretty common to see parasites as all black forms. Things that look blobby like larvae, spiders, imps and humanoids are all normal, so this isn’t enough info by itself. And you’re talking about a guy that can’t banish properly either, so who knows what’s around him.
Is is also common for a third party (i.e., me, in my experience, anyway) trying to remove an attachment to find it gets up in your face trying to scare you off. Points for having the cohones. 
You can ignore that, they are weak and insectile, no better than ticks, and all they have is mind games and lies, so don’t be taken in.
Ok so that aside lets get back to the actual issue…
So this is real, imo, and your intuition was spot on, which is a good sign. It’s certainly a good experience - In future you’ll remember this and act differently.
His assumption on why may be wrong, but the conclusion is reasonable … I actually hear a lot on this forum that the LBRP doesn’t help, so that might not be about your magick not working, as much as, LBRP is not the right technique for you.
Parasites that are fed over a longer period of time get “embedded” and stronger, making them harder to both find and kill. And I say kill because that’s the attitude I recommend for dealing with them from here.
Banishing without warding has limited effect. Imagine throwing a mouse out of the house and thinking it wouldn’t run right back in? Wards must be set to stop unwanted things coming in in the first place. Protective circles do this and I recommend having a permanent protective circle around your house and your bed.
So from here, there’s a better thread for ways to get rid of parasites to try - Forum Tutorials: Parasite Collection - #18 by Mulberry and I have linked my way, which is aggressive and I think appropriate at this point. You have made it abundantly clear these are unwanted via the LBRP and they ignored you, so by universal law you have the right to defend yourself and attack them back.