Good news, everyone!
I rang the department of street names and numbers and they explained that it’s royal mail’s fault, cause most companies use their database. Basically, they used to register regency buildings (yes I am fancy) as one property with one letterbox, because that way if post ever went missing they could be like “not our problem, one of your neighbours took it.” Anyway, then they had to change it and have all properties as separate, so they’d go and do audits, but occasionally if the occupant of a flat didn’t answer the door they’d just miss it off. So essentially many years ago someone lived here who was a lazy shrew and didn’t want to get out of bed and now I don’t exist. ANYWAY, the nice person I spoke to said they’d speak to the “royal” mail and I should exist again by Tuesday.
What a palarva.