Following some messing around, I have officially checked in and the apartment is good value considering I was 'upgraded' for their screw-up. Oddly my Marriott reservation was cancelled, which considering I have every intention of claiming the nights and points I jumped straight on.
An email to Agency 1, and a voicemail to Marriott H&V resulted in agency 1 saying "It's fine Marriott know and you will be credited", which I wasn't too confident about. Following 3 exchanges with Marriott after a lovely lady by the name of Priscila called me back and took all of the details, she has just emailed to say that an offline reservation has been shared. I am awaiting further details, such as confirming the number of nights etc, but assuming all is correct; this has been a mediocre experience. Messy service and a bit of hassle to make sure everything is as it should be; if it weren't for the upgrade, I wouldn't consider H&V amazing value based on this single experience.
I may try it again for a shorter stay, where I'm looking for a comfortable place to sleep for a few nights and am not so fussed about a few nights/points rather than a monthly hideout during the current crisis..!
"Hotels, if you hear me, please open again..!"