Beginning on March 2018, IIJMIO, one of the largest MNVO SIM operators in Japan, started screening credit cards linked to IIJMIO accounts once a month to ensure that payment methods are up to date and to reduce cases of expired cards being registered.
Japanese Announcement: www.iijmio.jp/info/iij/1523009739-15639.html
One unfortunate result of this new policy is that some foreign-issued cards are being flagged and are becoming unusable even though they were initially approved at contract start.
If your overseas credit card is not accepted, you will receive a notice by email and a bill by post. The bill sent by post is payable at your local convenience store so please be sure to make this payment as soon as possible.
If you have a Japanese credit card, a simple solution is to update your payment method to that card. As the IIJMIO website is in Japanese, please use this guide that H&R Consultants has created to help ease you through the process.
Changing Credit Card Bic_sim_iijmio_Important_Changes (PDF)
Please note that if you do not update your payment method to an accepted credit card or pay at a conveneince store, your service will be suspended at the end of your current cycle and the contract cancelled at the end of the next cycle.
If you do not have a Japanese credit card and your foreign credit card does not work and you wish to change your phone company please find other popular options below that may work for you. In addition to these options, there are also Softbank, Docomo, and AU, although generally monthly fees and cancellation costs are generally much higher than SIM-only plans.