12.5.5 basically bricked my iphone 6?

Hello,

I have an iphone 6 on Verizon that I accidentally updated to iOS 12.5.5 on Saturday night. Since then, my phone has been almost unusable: it cannot find, let alone connect to wifi networks (on the rare occasions that it does manage to connect to my home or work wifi, the connection drops every few seconds and is incredibly weak), it can barely connect to LTE and struggles to even get 3G, and my GPS is rarely able to locate me. When the GPS can find me, it can't keep the connection and turn-by-turn directions don't work. My phone's performance is generally much slower and spottier and when I called Apple for support it dropped the call several times.

I cannot downgrade to the previous update, nor do I have a recent backup––last backup was over 6 months ago and I don't want to lose photos I've taken in the interim. Apple gave me instructions for how to re-install this update via iTunes, but I don't think it worked properly––my phone woke back up from recovery mode, but it still has almost no service and the download appears to still be in progress via iTunes.

Is there any way to fix this? My phone was working perfectly before this update and is now almost completely unusable. Buying a new iPhone is not gonna happen as I already planned to never buy another Apple product again, but I expected to get a lot more life out of this phone before having to go through the time and expense of switching everything to a totally new system.