Cancelling Contract After Moving Abroad

Hello, 

Good afternoon,

I have moved from Germany in October. At first I thought it would be temporary, but now I have officialy returned to my home country (Brazil). I've been looking to cancel my O2 Mobile + Data plan I have signed up for in May 2018 (both mobile). I have read previous threads about the subject but I receive error messages when trying to download the forms/PDF files to be filled and sent along with a letter and evidence of movin abroad. I have a few questions:

1. Are those forms still needed or can I just write a letter asking for my number and data plan to be cancelled and authorizing the payment of the 3-month basic fee? 
2. If I need the forms, then I would like them to be sent to my email so I can speed up the process, since this letter will be sent from my home country (Brazil) and it takes longer than sending it from EU.
3. I have the Abdmeldung and a written english document from my parents guaranteeing I have moved back to my apartment in Brazil - with address, ID numbers, etc. Is there any other document needed so theres no confusion once the letter arrives in München? Keep in mind that my country is in crisis and each month it gets more and more expensive to send euro payments from here.
4. Should I give a specific date to terminate my contract or can I ask it to be canceled in the immediate moment of receiving the letter?
5. If theres any other fee left to be paid aside from the 3-month basic fee, will I be notified by email to make this payment along with the basic-fee? I no longer have a bank account in Germany, so it is very important that the transference is made at once.

One other thing is that I can't seem to find my contracts here in Brazil, there's a chance I have left in Germany. So I only have my name, documents and phone number (Handy und Festnetznummer) to cancel it.  Is that a problem? Can o2 help me recover any data missing?

I appreciate the answers to come