Also, software updates are painful. If your washing machine breaks, it's obvious why it's broken, and replacing it just costs money. But when software needs updating, it's unclear to the average person why that's the case. It doesn't rust or rot; why can't I just keep using it? And if I don't like the price of the update, migrating to something else is often a large project.
Maybe it would help to clearly state at purchase time something like "includes N months of updates"?
After a while in this business you start to develop a thick skin.
If you want to save yourself the hassle, factor the cost of maintenance updates into the initial cost, and market upgrades as big new releases like Windows or AutoCAD do.
Which product is this, by the way?
On the other and, that exact same customer already ordered and paid for updates. That's one of the reasons I'm annoyed to have had that update discussion.
It's an online appointment scheduling software, btw.
Oh, I thought it couldn't be appointmind, because on that website you literally say "We take care of software installation, updates and data backup.", granted right after saying "Monthly terminable".
I think your pricing model, customer flow, and messaging is incredibly confusing; and I don't think I would necessarily know whether or not ongoing updates are free of charge from your website.
I think the problem lies entirely in your marketing and presentation.
The trouble is exclusively with old customers that don't use the Saas, don't want to use it, and still run the software on their own server. They believe they bought the software and therefore own it. Paying again for something you own is, understandably, not something people gladly do. But then again, software isn't a thing, it's a work in progress. A concept hard to grasp for some people.
1.) People are often horrible communicators.
2.) Marketing copy very rarely (if ever) discloses there will be a fee for updates.
3.) Updates are confusing and nothing is standardized. Some companies offer free updates forever. Others charge for updates. Still others disguise updates as new versions.
But in the end, some people will just try and get free stuff. Just tell them that doing business with you has a price and that otherwise they can bring their business at someone else's shop.