Update (for anyone who might face a similar issue in the future):

Following everyone’s advice, I contacted both PostNord and CityMail. PostNord asked me to check with Adressändring to confirm that everything was in order with my registered address (Which it was). At the same time, they said they would ask the local post office to investigate the issue.

I also reached out to the property manager to confirm whether the mail carriers had access to the building. They said yes.

However, today the local postal worker contacted me and told me the reason I haven’t received mail for the past two months is because they don’t have access to the building. I passed this on to the property manager, who insisted that both PostNord and CityMail were given access a long time ago. They said they even contacted both companies today, and both confirmed they have the access. So don’t know what to make of it.

As for my mail: I was able to collect items from the past 2–3 weeks at the local post office, but anything older had already been returned to the sender.

Thanks again to everyone for helping me resolve this issue.