I cant activate a multicard sim

Hi, 

I am extremely frustrated because for a week I have been trying to call the customer service everyday to activate a multi card sim. I cannot activate it via Mein O2 because to register it sends a message a to the number that’s not activated yet? 
 

i can’t reach a chat service online. 
 

Now my old SIM is cancelled and I can’t even make a call to the useless customer service. 
 

How can I activate this SIM card?