I looked into it a bit. It seems like it’s related to some new laws introduced last year:
Regulations for Telecommunications Enterprises Using Designated Databases to verify User Identity
Article 4:
Telecommunications enterprises shall process applications for telecommunications services as follows:
[…]
3. For non-ROC nationals: Verify the entry and exit status and the validity of the document using the designated database specified in Subparagraph 3, Paragraph 1 of the preceding article, based on the passport number and nationality code, or the Residence Permit number.
Article 5:
When processing applications for telecommunications services, telecommunications enterprises shall, in addition to verifying the subscriber information pursuant to the preceding article, further assess the subscriber’s risk level using the Integrated Anti-Fraud Risk Database with the following identification information:
[…]
3. For non-ROC nationals: Passport number or Residence Permit number.
Article 8:
After the implementation of the Act, telecommunications enterprises that provide prepaid card services to non-ROC nationals in accordance with Article 22 of the Act shall conduct monthly batch inquiries via the Immigration Database to confirm the subscriber’s entry and exit status and whether the subscriber has overstayed or exceeded the permitted residence period.
For prepaid card services provided to non-ROC nationals prior to the implementation of Article 22 of the Act, telecommunications enterprises shall notify subscribers to provide the identification information required for verification via the Immigration Database within two weeks. Once the subscriber provides the required information, telecommunications enterprises shall verify and register the information, and thereafter conduct regular inquiries in accordance with the preceding paragraph.
The notification procedure specified in the preceding paragraph shall be outlined in a notification plan, which telecommunications enterprises shall submit to the competent telecommunications authority for recordation within two months of the implementation of these Regulations. Any changes to the plan shall also be submitted for recordation. Telecommunications enterprises shall complete the notification process in accordance with the plan.
If, during the verification specified in Paragraphs 1 and 2, telecommunications enterprises discover that the subscriber has exited the country, overstayed, or exceeded the permitted residence period, they shall notify the subscriber to reverify and register their identification information in person at a store of the telecommunications enterprise within two weeks. Before the specified period expires, telecommunications enterprises may restrict certain functions of the telecommunications service. If the subscriber fails to complete the reverification and registration process within the specified period, telecommunications enterprises shall restrict or terminate the provision of telecommunications services in accordance with Article 22 of the Act.
Article 22 here seems to be referring to:
Fraud Crime Hazard Prevention Act
Article 22:
During the period providing prepaid card services to non-Taiwanese users, telecom businesses shall check whether such users leave the country or overstay by connecting to the database specified in paragraph 1 of Article 19.
If it is discover that users have left the country or overstayed based on the inquiries in accordance with the preceding paragraph, telecom businesses shall restrict or suspend their prepaid card services.
If non-Taiwanese users mentioned in the preceding paragraph re-enter during the valid period of prepaid card services, after applying for the verification and registration of users’ identity with telecom businesses, telecom businesses may continue to provide the initial telecom services.
I’m curious now if this happened because I left the country on vacation (the dates seem to match up, since I left on the 13th and it stopped working around the 27th or 28th). That could certainly get annoying if so…
…especially if the notification is done via SMS by a company that doesn’t allow foreigners to have roaming on prepaid SIM cards.