Need help on communications from a remote site

I helped install an off-grid system on an island off the coast of Maine, using Schneider Electric equipment with a Discover lithium iron battery. Our plan was to use the InsightCloud website to monitor the system. Although the island is remote, it does have cell service connecting through a cell tower on the mainland. We installed a Netgear modem with a charger and a circuit breaker and powered it off the battery. The problem is that it won’t stay connected, and once it disconnects it has to be manually shut off and restarted to reestablish the link. This makes it non-functional in our application. Any suggestions or ideas about how we might set up reliable communications at a low cost? (Starlink is not an option as it is too costly for us.)