@Matthew92 "But the fact he has done this surley is a breach of T&Cs on some level?!"
Not really. Verbal agreements, even when written in a message, aren't binding. And as I mentioned, hosts are under no obligation to agree to alter booking dates. There are unfortunately bad hosts out there, just as there are bad guests. Guests have gotten burned by hosts who tell them they will give them a refund, because there was some legitimate issue, like the guests arrived to find the place filthy, or the appliances didn't work, and the guests don't realize that in order to insure that they receive a refund, they actually need to cancel and leave, not trust the host to do what he said. I should hope that most hosts are trustworthy, though. I would certainly never promise a guest something and then renege on it.
But a host who ghosts you for months, refusing to respond, and even ignores communications from Airbnb, shouldn't be allowed to remain on the platform. It's pretty outrageous that Airbnb didn't offer to cancel your booking and refund you when they also couldn't get a response. (It occured to me- maybe the host died? Do they still have an active listing, with recent reviews?)
But customer service is abyssmal these days, staffed by outsourced, know-nothings who give out incorreect information and advice- they are next to useless, and often worse than useless.
You aren't meant to be checking in to this place in a week, though. Your booking was cancelled. You no longer have a booking there.
Try contacting Airbnb through their Twitter account. They don't like their dirty laundry aired in public, and you might have better luck there.