XING ProBusiness

I would like to become a XING ProBusiness member. What will happen to my Premium membership?
What happens if I want to purchase XING ProBusiness as a basic member?
Can I use another billing address for the XING ProBusiness add-on?
How do I cancel XING ProBusiness?
How can I pay for my Premium membership and/or XING ProJobs with PayPal?
Our partners in receivables management
Why have I received a letter from a receivables management company?