I doubt this is going to be resolved and I can explain what likely happened (as I work for a domain registrar and hosting company):
Someone forgot to renew the domain. This can cause more than a few problems (ignoring that the site would go down) because when a domain expires, it goes into something called a "Redemption Period". This is a time where it's still registered to you, but doesn't work anymore. The major issue with this is that getting a domain back out of Redemption normally costs a lot of money (somewhere between £80 and £200 depending on the registrar) and then the renewal cost on top of that.
If you don't pay for the Redemption clearance then you have to wait out this period until the domain expires entirely and goes back on the open market. At this point, if the domain is popular, it'll immediately get snapped up by any of those nasty "domain squatters" who basically try and extort the domain back to you for at least £2000 or more (depending on how popular the domain was). If you're a business then you'd take them to court at this point or get a WIPO issued, but that's beyond what I'd expect the BTTR guys to go through as it's costly and potentially requires lawyers.
TL;DR: Domain expired, it'll cost lots of money to get it back. Chances are that won't happen so getting used to back2roots.abime.net is recommended.