SEPA Mandat

Hello!

I want to ask with regard to a situation is happening to my O2 line:

Although O2 have already deducted from my bank account the payment for march, I've received a letter asking to send the SEPA signed through Fax, or to open a website. When I opened the website, it showed a message stating “Operation successful”. Two weeks afterwards I received a second letter asking for the same.

Is it required for me to send a SEPA Mandat through Fax? (In 2021 almost nobody has such device, including myself)

Can I pay with a standard bank transference?

Can O2 activate an option to send the SEPA Mandat through email/ upload it to Mein-O2 for other users?

Thanks in advance for your help