How to activate unlimited data package for existing prepaid customer?

do you mean the o2 Prepaid Max?

Yes. I tried via web, but unfortunately couldn’t. 

Have you logged into the customer portal with your phone number?

Shows this below error message

Auf dem aktuell verwendeten Account ist kein Vertrag mit Laufzeit hinterlegt. Bitte loggen Sie sich mit einem entsprechenden Account ein, um die Produkte mit Bestandskundenvorteilen kaufen zu können.

Mit einen Prepaid Account kann man keine Partnerkarte bestellen. Logge dich aus, und bestelle über diesen Link: https://www.o2online.de/mobilfunk/rabattaktion/

This is seems like oredering a new sim card. I am currently using o2 sim card. I need use this offer for the same number. How can i do that? Can i do it for the same number. 

No, this doesn't work for prepaid. You can conclude the contract and then take your phone number with you.

its so sad. I need the same number. is there any possibility get the same number with another contract having unlimted package?

As written, you can then port the phone number. Or you can switch to the o2 Prepaid Max, which costs EUR 74.99 for 4 weeks.

I could see one option in the checkout page for porting. I need to specify the provider name for the number. Can i choose o2, Tchibo -O2DE as for o2 provider?

Should i choose this option for existing

o2 customer

You first have to conclude the contract and after activation you order the phone number to be ported from the contract in the customer portal.

Hello ​@josejohnyp, were you able to place the order and did everything work out so far? 🙂

Kind regards, Ines.