@fdi Thank you so much for your help! Do you know why only SpeedOn is possible?

might it be that you both are not talking about the same?

If I understand "top-up" system correctly you are talking about trying putting money on your prepaid balance to pay the next 4 weeks for your existing rate e.g. via www.telekom.de/aufladen,  but the system only offers 30 EUR as an option correct?

If yes @fdi  actually did not understand it correctly, cause I guess he thinks you need more data volume for your existing rate (e.g. + 5GB up/down). this would be the "speedon" part which is - indeed - more expensive in comparison to the included data volume for your existing rate. 

but why telekom.de/aufladen only offers 15/30/50 EUR and no option (at least I did not find one at the first sight) I also do not know. Easiest way: buy a Telekom (! no other vendor) prepaid code somewhere in the internet or at a gas station or supermarket or whatever, they often offer the possibility to chose the amount or give you 20 EUR gift cards (e.g Cyberport.de offers 20EUR Telekom prepaid cards).

Thank you for your message, @Wesley1

You've already been given the correct answer.

Apart from the top-up cards in stores, in your case there is only the option to choose 30 euros for automatic top-up. But that's no problem. If you set up automatic top-up "Top up when your tariff/option is due and the remaining credit on your prepaid card is insufficient" then you will probably have free credit for the next month after 8 weeks.

You don't lose any money. Does that help you?

Kind regards

Carolin L.