Hi Basti,
herzlich willkommen im Forum!
I'm not sure how long blacklisting are generally imposed, but have you tried using your current CC? If you are indeed blacklisted, you won't be able to use it at all.
Besides, you don't need a CC in order to purchase a mobile phone. I acquired my first Softbank iPhone paying all monthly installments as well as the fees in cash.
Another option might be debit cards (Visa, Rakuten, etc). I don't if they are affected by blacklists.