I really feel like there are four issues at play in all of this.
The price rise
Personally, this is the one which, although I can understand the issues it's causing for some, is in my opinion, the least controversial of all that's gone on over the last few days. Things get more expensive, the product is very different to what it was since the last increase in price, and so personally I have no problem with it. As long it goes hand in hand with a discernible and ongoing improvement in the quality of the product. There's work to be doing, rough edges to smooth and features which need adding. I do see why this may cause people to move away from Invision though - everything has its price and there are (and always have been) cheaper (and even free) alternatives.
The support change
On the face of it, this looks terrible. But in a way it's all in the telling as it's not really a big change, assuming it works as Invision are saying - eg things that need a ticket will end up in one. For me it's one of those that needs to be given a chance to see if it works as advertised or not - if it ends up being poor then it'll need addressing/reverting to tickets urgently.
Communication
This leans into everything else really. Had the price rise been communicated in advance, then that may have mitigated a lot of the upset it's caused. If the support changes had been communicated more clearly, that would also have stopped so many people assuming various different versions of what it is that Invision are apparently planning to do. It's an ongoing weak point with Invision in my view. There's no doubt that Invision make us feel less valued as paying customers than anyone else we spend our money with, sadly.
Does Invision care?
This is often about communication and the perception that it gives. I mean how many times can you screw it up so royally that you leave your customers confused or angry or both? With Invision it's frequent, it's frustrating and it's entirely avoidable. If you refuse to learn, refuse to take it seriously and don't change the way you do things after so many years and so many occasions, why should your paying customers keep giving you the benefit of the doubt?
It's not enough to say you care as you're picking up the pieces of another mess, or arriving back onto the scene of another feature left on the shelf for months with zero communication (think mobile app, as one example). You need to show you care, and you need to step up and own the problems that are of your own making by showing some flexibility. EG - maybe look at a longer period of 6 month invoicing for existing customers who request it, offer a discount code for those with renewals within 3 months or something - just do something, anything to show it's not all pr style fake 'regret' just to play for time until everyone calms down or gives up. It's very little effort on your side in the great scheme of things, but could make a massive difference to the customers you're doing it for.
Oh, and finally (long post, sorry), look after your third party developers - you need them, so show some gratitude and a spirit of partnership by working with them.