Dear @Yudhajeet ,
first of all, welcome to our forum. Nice that you have found your way to us. :-)
You have to contact your old provider to inform them, that you want to take your old number with you to your new provider o2. There you can ask how much a porting will cost you. Ortel will bill the porting.
When your new SIM-card at o2 is active you can register for “Mein o2”. Either in the onlineportal or in the app you can assign the porting.
Do you have any questions about using our community? Then have a look here at Neu in der o2 Community? Die wichtigsten Funktionen und Hinweise auf einen Blick. There you will find all the information you need to use!
Kind regards,
Andrea