Toilet training help wanted!

A bit of backstory here. We got our border terrier pup in June - he's currently 17 weeks old and is having issues with peeing inside.

When introducing him to the house we used bells for signalling that he needed to pee. This worked quite well - he would ring the bells and be let into the toilet to go on a pad. He was also being taken outside at regular intervals where he would pee well enough.

We then spent ten days away from home in July. Not ideal but it was due to some weddings lumped together so we had to roll with it. Luckily it was during the massive heat wave in Scotland so he spent most of his time outside and by the end he would whine whenever he needed to be let out when indoors. Over the ten days only a couple accidents inside when visitors got him very excited with play.

So on returning home (perhaps this is our main mistake!) we decided to try hanging the bells on the front door and going outside every time so no puppy pad use. Unfortunately by this time he seemed to have forgotten about the bells completely (they weren't needed up north due to the above) and would head to the front door and then pee in the area next to it. This is an area he never uses otherwise so now we feed him here to discourage its use as a pee spot.

The main issue now is he never asks to pee. He will sit in a corner and look at us (we do get him to ring the bells whenever we take him outside), then if enough time passes he has taken to going into his crate and peeing there, which he never does at night. He also retreats to a corner whenever he gets the idea that we're taking him outside.

So my main question is what would our best strategy be going forward? Start over with the pads? Keep going with the bells when going outside and not try waiting for him to ring them on his own for a while longer? Why does he seem afraid to go out? He always gets treats for peeing out there and enjoys walking around the area. Are we expecting too much at this stage??

Thanks in advance!