Dear Alzhao,
Thank you for your message.
I would like to highlight I was referring to the German-based company (called T-Mobile, or Telekom). It is sometimes confused with the same* company T-Mobile, based in USA.
In any case, I was able to solve my problem as stated in: Mifi: LTE connected but no Internet - #26 by sebastian (link for future reference)
*I doubt on calling “same”, because they only share the name. Maybe the investors and stake-holders. But they are two different companies from a technical and commercial point of view. I used to be client of USA_T-Mobile. Which made no difference when I started to be client of Germany_T-Mobile
With best regards
Sebastian