Changing my VAT EU no

Hi, I wanted to change y VAT EU number, all I need is just put two letters before my Vat no. But the system doesn't let me do it. How can I change it so I can put my VAT EU number at the invoice?
thank you in advance

Hello,

For this type of request, I invite you to contact our billing department so that we can provide you with an answer adapted to your situation.

^FabL

Problems with the domain. Write phone numbers or mail, where I can write. Tech support throws me to others. I've contacted you for nothing.