Wrong VAT Registration No. in invoice to customer

Dear experts,

We have a company in country CZ that sells goods to customers not only in CZ but also in SK.

Now when an invoice goes to a customer in SK the "VAT registration number" of "company CZ" is on there which is incorrect.

On the invoice there should be the "VAT registration number" of SK.

I saw that in OBY6 one is able to maintain the "VAT Registration number" on Company Code level:

I found 2 company codes, one for CZ and one for SK. Both company codes are maintained, also the "VAT Reg. number".

So how come I do not have the SK "VAT Reg. number" on invoices to SK customers?

Where does SAP decide which VAT Registration number to put on the customer's invoice?

Does it start when a Sales Order comes in?

Thank you for your help with this,

Peter