We are charged $2224 (more than double)? How is this normal?

As of our last month bill we have around 188K contacts + 3 additional users. We are being charged 2224USD!
This has been happening for a few months now. Is this normal? We expect the bill has to be 199$ (max classic)+ 90$ (3 additional users) + 800$ (for 200K users) = total of 1089$ (+tax maybe)

But we are charged 2224$! Can we get a refund for all the previous months when we were overcharged?
Am I wrong in feeling a bit outraged?