I’d say that’s a fair assessment. The cutoff date for activating 3G modules with new Alarm.com accounts was June 31st so it’s long past. If we could, we would let you do it but it’s not in our control.
You will eventually have to upgrade to 4G anyway even if you stick with Frontpoint as the 3G sunset is just 2 years away (Feb 2022) and 3G service will degrade before that in some locations. But I feel your pain.
So given that you’ll have to upgrade either way, I recommend doing an apples to apples comparison to determine which is the better fit for you. Luckily, I just happen to have such a comparison! 
In the long run you’ll save money even with buying a new panel. And you can spread it over 12 months with Klarna if you’d like. (requires approval by Klarna)