[redmex2]

You aimed too high, trigger an investigation that linked together the accounts (when they didn't really care before) as well as new one
No, amazon can't see your MAC address (unless you're using the app on the phone, then maybe it's doable, but a website cannot access those information)
If you're using a VPN, maybe they blacklisted that range of IPS
If you're just resetting your router for a new IP, they could've blacklisted the area that geolocates the IP
Or, most likely, you always had a flag on all accounts and just went under the radar with low refunds until now, but you're red flagged now, and it's gonna be a pain to get a new account

So the problem is propably the internet connection?

Yea, i used mainly my router and re-connect, to get some different ip-address.
also used internet from smartphone sim via hotspot , both ways worked fine, both ways are now broken

Sometimes the account's get closed instantly, but sometimes the account is created and the money from my payment method gone and product will delivered.
Why they let me create and pay these accounts, if im red flagged? or is this just about fraud protection on refunds?

Didnt found a ways right now, to avoid this hole i'm in currently. guessed to reduce the money-amount again, but sounds like this wont help.

Just out of curiosity, what method did you use?

Order 200-300$, grab the package.
Contact amazon -> package was delivered to me, package seems ok, no damage, but the item is not inside.
That's all.