I've restored the comments and feedback page functionality to this site by creating a new MySQL database. Frankly, I was tired of waiting for my hosting provider to fix the problem, which has been dragging on for over a fortnight now.
Unfortunately it does mean that all the previous comments that were made have been lost, but if they are ever able to get the old database back then I will merge the old comments into the new database. I'm not at all happy about having lost the comments but I'd rather have a fully-functional website. The whole episode has been a complete nightmare and I just want to get back to normal now.