@Charlie417 As a guest, you always have the right to cancel. The host cannot prevent this. With limited information here, I'm guessing that what the host meant was that they weren't allowed to cancel, because Airbnb penalizes hosts for doing so.
It's a moot point now, because the stay was never cancelled in any capacity. It wasn't the host that marked the stay as "completed" - that happens automatically from Airbnb if you don't follow the cancellation procedure. If you had placed the booking before 14 March, 2020, you would have been eligible for a full refund from Airbnb, if you had followed the instructions for extenuating circumstances. But any informal arrangement you make with a host outside of Airbnb's protocol is non-binding. That means it's really at the host's discretion whether to offer you new dates, give you money, or simply do nothing.
At this point, this is no longer an Airbnb issue, since your rent is already paid out and you don't have an active booking in the system. I don't think there's any kind of help you can get from customer service at this point, a year and a half after the aborted stay. That leaves you with no leverage, so you'd have to persuade the host that you'd be a delightful guest to accommodate despite your stay bringing no additional income. That takes a special kind of charm which is instantly negated if you give the impression that you're trying to seize last year's paychecks. So if you want to pursue this, do keep in mind that while you only suffered the loss of some disposable income that you'd already allotted to a holiday, your host lost many months of income to the lockdowns and probably hasn't recovered enough yet to start throwing money at would-be guests from last year.
