Hi there, Mattcais! Grandfathered plans can be kept as long as the device is not changed, or if the new device is compatible with it. In this case since the flip phone that you bought is also not compatible it would mean that none of our currently available devices would be compatible with your plan, and you would have to change it. If you still want to return the device (and it hasn't been more than 7 days from the day when you processed the order), please send us a private message so we may work directly with you.
You can send a private message by clicking on my name, then selecting the message option from the profile page.