Before we start this, I have paranoia issues (doctor diagnosed, not self-diagnosed) so things might at some points seem like an extremely far reach, but please bear with me.
I bought an AV yesterday (prefer not to name it), after reading site reviews about it and getting a few recommendations about it. But after buying it, I stumbled across some user reviews and a lot of them were talking about abysmal customer support and shady business practices. Not only that, but when making an account on that AV's site, it was riddled with issues ("Invalid email"), and then after somehow making an account, when I tried to log in, they kept saying "invalid username or password". So I clicked on the "forgot password" option, entered my email and submit and they never sent me an email to reset the password. So I just logged in using my google account tied to that same email. After that, I downloaded and installed it on my Windows PC and Android phone, and unfortunately it was then I saw the user reviews which were abysmal, and I realized it was kinda poor for me too.
I emailed their customer support asking for a refund, and removed it from my phone, and uninstalled it from my PC. Then I had to restart my PC to complete uninstallation, and after restarting, the AV was back on my desktop, and on the "apps" part of settings. So I google searched and downloaded their own uninstaller and uninstalled it, and after it uninstalled, it said "uninstalled with errors, contact customer support to complete uninstallation". I felt I can't bother with that, so I just to restarted the PC, looked to see if it was still there, and then clicked on "This PC" and typed in the AV's name in the search tab and shift deleted every single file with the name of the AV.
After that, I restarted again and realized my PC was considerably slower. BIOS time before installing the AV was around 2 seconds, but after installing and uninstalling the AV, BIOS time is now 4 seconds.
Now all this; the shady business practices, the poor customer support, the uninstalling difficulties, the difficulty and errors faced when trying to make an account, and the BIOS time slow down even AFTER UNinstallation, makes me worried about if these guys are still in my PC and phone and are maybe accessing the deepest corners of my pc and phone. I gave them access, what's to stop them now?
Can they still access my PC, phone, and also maybe my google account? Do they still have access to my PC and phone? Could they hack me or something?
And if so, how do I completely purge their existence from my phone and PC? How do I get my PC back to normal? How do I stop them from accessing my PC? How do I make it as if it was never installed in the first place?
P.S. This AV is quite a reputable software, review sites love it always gets great reviews from testing labs and so on and it has hundreds of millions of users worldwide. So it's not some unknown AV.