Post Studio ‑ Social Auto Post

I used this app for at least two years. And it does what it promises, no problems.
But what angered me happened at the end, when I signed up it was $9.99 a month, now the moment I cancelled the plan I saw that at some point in time they had changed the price of my plan to $7.99 behind my back, but they continued to charge me $9.99 for who knows how long?!

Support conceded that they made price adjustments along the way and that there was some 'miscommunication', offered some credit that I won't use because I was moving to another app, and more importantly didn't mention for how long this had been going on, so I won't know how much I over payed.

I know is "just $2 extra a month" but it's the principle, and it doesn't feel nice.