Getting into the building was a horror show. Luckily, a couple who actually got the email with the two codes let us in. We ended up splurging on the hotel next door after we barely were able to use their lockers (key jammed) to store our luggage while waiting for check in. We were tired, and not hearing anything back from the hotel. We couldn't even make calls as travelers from out of the country.
The service was awful, especially considering how helpful the staff at the 5-star hotel next door were (this is before we booked a room). I swallowed the cost and we used it as a chance to live lavishly, despite not being 5 star travelers. I never did get a response back from Lisbon Old Town Guest House.
Ironically, we were having coffee outside the "nice" hotel next door waiting for our taxi on our way back home, and I see two travelers struggling with the Lisbon Old Town Guest House door. I waited 5 minutes because I'm socially awkward, but it was clear they weren't getting into the door.
I came up to them and said we had the same issue. I wrote down the codes given to me by the other travelers and felt a duty to pass it on. He showed me their email and it only gave them the door to get into the hotel on the second floor, and nothing for the main entrance (different codes).
They were very grateful, but this is clearly not just a one off issue. If you're landing here after any type of distance travel, be ready for a major headache.