That agent has no freaking clue what they are talking about. I have had hotel stays applied to my account and it pushed out my expiration. I also use Teleflora for Mother's day since they typically have some big bonus on the order.
I had a friend of mine whose miles were going to expire earlier this month and he said that he got this email in March:
YOUR MILES EXPIRATION HAS BEEN PAUSED
We appreciate you flying with us and in consideration of current events, we are pausing the upcoming expiration of your miles. Your miles now will expire at the earliest 5/31/20.
- The FRONTIER Miles Team
Who knows if they plan on pausing for a longer period of time. Even Spirit has paused expiration until the end of September.