iPhone 6 factory reset itself, forgot its wifi password and is now unusable - help?

Good day to everyone,

Recently my iPhone6 has been displaying messages that "storage is nearly full", and I've deleted as much as I can without removing things that I need. Photos admittedly takes up about 5GB (huge, I need to sort) but everything else such as apps probably all amounts to 6-7GB. But the storage space says that 11GB have been used up, and whenever I delete anything, no free space becomes available.

Last night I had to restart my internet, and my iPhone6 needed the password to sign back in, but it's now not accepting the password, saying that it's incorrect, even though all my other devices can connect to it.

I went to bed, and this morning decided to turn my phone off and on, as you do when something doesn't work.

To my surprise, my start screen said "Hello" and then "Hola" - like I'd started my phone for the first time.

And guess what? It needs a wifi connection to start, which it can't because it won't accept the password.

I've not yet connected it to iTunes through my cable - that's the next task, but in the mean time, has anyone else come across this and is it just time to move on from this phone? (Personally I don't think 2 years is long enough for a piece of hardware to become obsolete). Or is there anything that can be done?

Cheers in advance!