Mutuelle

Hi - I recently got an invoice/bill from my new mutuelle. How do I pay it? 

They sent me an automatic deduction form, but I don't want to set that up ... I've looked on their website and it was really confusing. Can I just pay using internet banking? But how would they know it was from me? There are no instructions. There is an orange tear-off slip at the bottom of the page with their IBAN etc ...  What's the easiest and fastest way?

Thanks for any help.