Are you talking about the due date laid down in the debit note (Direct Debit/”Débito Direto” in Portuguese)? If so, indeed you can adjust the due date:

You may choose one of these days of the month: 

4th, 12th, 1st, 19th, 28th

The 1st please

I am just a normal customer like you.

To do so, you should write a private message to @Fórum (NOS profile) with your personal and contract data (NIF, client ID number, Name, etc.)

Hello,

Thank you for reaching out to us @Georgina Edwina Egbeama.

@CP001 gave a good help regarding this matter. Please send us a private message to the @Fórum profile with your NOS Costumer number and NIF.

Thank you