Well it should just work, but i know the way it is on Xbox, we can just switch our region, and when we add any DLC or add-ons, it remains there for the game to use no matter which region we switch to!

perhaps thats worth a shot, other than that, not sure how its supposed to work on PS

You have to contact support. DuroNL is right that you can change regions for free, but an account stays region locked for the actually upgrading (once upgraded it will take the dlc's etc over to all regions.

So an EU-region account, can be used on the US megaserver, you can also buy crowns through any source and use them to upgrade your account in the crownstore. However, you can not upgrade the account with an US-region locked upgrade.

So it is only bout the actual upgrade process.

The reason for this is that there are a lot of shady resellers. By regionlocking accounts they can sell, they are limited in hiding thier tracks. Support will tell you if you really bought the account legit. If thats not the case, they can help you in getting a refund and a new legit copy (I don't know how it works on PS4, but a friend of mine had a bad account on the PC. his account was locked, but once he bought a legit copy, he could use it to tie it to the existing account and continue playing his characters). If it is a legit copy they can also assist you in the update process.

As this is an account issue, other players can't help you.