I hope you copied this letter to all carriers all over the world. Do a search, everyone is taking the same steps although the timing varies over the next few years. Do a search and if anyone is letting you activate your older 2g/3g non-VOLTE phone go ahead and switch. But you'll be writing the same letter to them before long.
I can guarantee you Verizon knows exactly what it will cost them. Just like they did when the big black things that sat on the table that you stuck your finger in and turned to dial a number were no more. Technology changes. Like it or not we need to adapt.
I did a quick search and found plans for as low as $2-$3 per month depending on useage. That's cheaper than you're paying now.