Well I'm absolutely shell shocked.
We wrote a very fair email back to the original contact as I posted above. We did say how happy we were with them so far (as inexperienced FTBs) and how we'd like to continue, but thought as a gesture of good will they could give us the wills free of charge (c £300). They've emailed us back and said they no longer wish to act on our behalf, said nonsense about 'demands' etc.
I'm ****ing fuming. This actually came through as we were going through our mortgage application on the phone with Nationwide. Absolute ****ers
They're mental if they think this was the best course to take.. the mind boggles. Our email was extremely fair, we accepted human error happens, there were no demands, it was extremely reserved and put forward as 'this has caused us unnecessary stress, but let's get on with it and move forward'. FFS