One suggestion is simply increase the price. Price is strongly correlated with quality of customer. Price also acts as signaling that this is a tool for professionals who make actual money and so shouldn't be bothered coughing up something trivial like $100 for a subscription. You end up making more with far less customer support.
It can backfire when the new price point bumps it into a different category of decision making, though. For many, a $20/month product is an easy decision but $100/month price tag bumps it to a point where it becomes a more complicated decision making process. If you're not careful you can easily raise prices so much that people decide to jump to a more full-featured competitor product.
Projects like this one that are personal/side projects have an additional risk of raising prices: If the product becomes expensive, many people are going to notice that it appears to be highly profitable while also being within the realm of what a single person or small team can produce. Competition starts appearing quickly and you're back to cutting prices to stay relevant.
Finally, higher prices come with higher expectations from your customers. Whereas previously they might shrug off a slow response to a customer support request at $20/month, their $100/month service might lead them to expect more customer support, not less.
There are several indie SaaS companies that get posted on HN from time to time that take the opposite approach: They offer a low price but they're up front about what to expect. They don't try to pretend that you're getting world-class reliability, uptime, or support, but they do commit to offering a good service at a fair price. They could raise prices to match competitors, but now they're playing a very different game with very different expectations.