(twitch) why can't you change your email?

I have the following problem that i can't change my email. Does anyone know how I can prevent it? I enter my other email, everything is saved. But then it will revert to my old email.

https://telekomhilft.telekom.de/t5/Alles-andere/Twitch-E-Mail-kommt-nicht-an/td-p/1439031

and only once in 24 hours, so look where the confirmation email has gone.