Topping-up T-mobile outside Germany

[inquisitor]

Once the SIM has been deactivated, it can't be reactivated anymore. There might be exceptions, if you request reactivation shortly after deactivation, but after years there's no chance. The phone number could even be reassigned to another customer already.

But T-Mobile's rates are completely unattractive, especially for visitors, who can place international calls for a fraction of T-Mobile's rates with solomo or Fonic.