If you have qa enabled you don't need the 999 downgrader. just use rebug 3.55.4 rex to downgrade to 3.55. Once you're on 3.55 open up your rebug toolbox and find Dispatch Manager Access and enable it. Exit toolbox and start up Chaos Air Bringer.
There are tutorials on how to use Chaos Air Bringer. One last thing you don't need to completely change your entire mac address just the last to digits will do.

thx bro, ill try it tomorrow (21:57 in germany)

should i be in dex or cex mode?

go to cex before you downgrade.

so, i need to rewrite Target ID in Flash: Convert PS3 toCEX/DEX if valid dump is provided.
but i dont have the flash dump anymore because i dont jailbreaked it mysef

You don't have your flash dump anymore.
I'm not 100% sure but there may be a way to downgrade from 4.46dex to 3.55dex assuming you're even on dex.
I can't help you with that so you're just going to have to figure it out on your own.
All I know is as of now you have to be on 3.55 to change your mac.

hey guys, today i wanted to play Bo2 zombies and when i signed in it says that this console is banned from playing bo2 or something like that.

Can anyone say me if its a CID or MAC ban?

The only way to know if you are mac banned is to use a valid CID, Don't change your mac address unless you are a %100 sure that you are its very rare to get mac banned from BO2 thou and i have been CID a lot from BO2 but not mac banned. So like i said don't change your mac address unless your certain that it is banned as you will be just wasteing your time.