As this is mainly a peer to peer support fiorum, we are not privy to FiOS business decisions on service offerings.
You might want to try calling in to customer service to see what options you have.
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This tends to happen if you're on a BPON ONT. Verizon will require people to upgrade to 300Mbps for a month to cover the cost of installing a new ONT, and for installing Ethernet cabling between the ONT and your router. You can downgrade after the 300Mbps installation occurs at that point.
SInce you're transitioning to Frontier, however, you may want to either order it now, or wait until after April 1st, when the Frontier migration completes.