I think you might be mistaking the monthly fee with the initial $20 auto-pay amount they charge to maintain a positive balance in your prepaid account. The typical plan we recommend is the Maker Flexible plan, which is $0.60 per month (whether you use the card or not) and then $0.40 per MB of actual data usage. Most of our loggers (when transmitting at 5 minute intervals) use about 10 MB per month, so the total monthly fee for each station is around $5.
You can “pause” the service through the Hologram website dashboard, but all that does is prevent your station from being able to make a connection to the internet, but you’ll still be charged the $0.60 monthly fee even for paused stations. If you deactivate the card for winter to avoid the montly fee, then you can’t reactivate that same card in the spring, you’ll have to buy a new card ($5), swap it out with the physical card in the station, and pay the initial activation fee for the new card. So if you’re not going to be collecting data over the winter, it’s easier to just turn off the Mayfly logger station, keep the cards active in you plan, and just pay the $0.60 monthly fee until spring and then turn the Mayfly stations back on when you redeploy them and everything will operate like it did the previous year.