Prepaid SIM cannot connect to any network abroad (roaming enabled, multiple countries tested)

Hello,

I’m currently experiencing an issue with congstar prepaid SIM cards when roaming abroad.

Situation:

• The SIMs are used outside Germany (tested in Vietnam and China)
• Devices: iPhone and Android (multiple devices tested)

Observed behavior:

• Roaming is enabled on the device
• Available networks (e.g. Viettel, Mobifone, etc.) are visible
• However, the SIM cannot connect to any network (“No Service” / registration fails)
• Manual network selection also does not work
• Same issue occurs across multiple countries

What I have already tried:

• Enable/disable roaming
• Restart device
• Manual network selection
• Test SIM in different devices

Question:

• Is roaming enabled for congstar prepaid SIMs in countries like Vietnam or China?
• Could there be a roaming block or missing activation on the SIM/account?
• Does the SIM need to be activated in Germany first before roaming works?

Any help would be appreciated. Thank you!

Hi,

Thanks for the reply.

To clarify the situation: I’m not fully sure whether the SIM was successfully activated in Germany. A friend brought it to Vietnam for me and mentioned that the KYC (Video-Ident) was completed.

However, the current behavior is:

• the SIM can detect available networks (e.g. Viettel, Mobifone)
• but it cannot connect to any network at all (no service / registration fails)

Based on this, I believe the issue might not be related to datapasses (since even basic network registration fails), but rather a possible activation or provisioning issue.

Could you please check if the SIM is fully activated and allowed to register on foreign networks?

Phone number: +49 xxxxxxx234

Thanks!