I think its impressive that you get a promotion yearly since 2014!

But I think you are underpaid as an MX11. I'm a MX12 equivalent but I take quite abit more than you do as a MX11. I have roughly the same years of work experience you do, I started on Sep 13 and I'll be 28 this year. My job does not require me to have specialized skills; hence, no special salary structure applied.

Anyway, MX11-equivalent in my workplace draws somewhere from 6-9k. It could be that your yearly fast-tracked promotion does not sit well with the justifications on big revision to salary. So you could be paid at the salary floor of your MX11 rank. I'm sure MX11 salary ceiling has a pretty attractive sum too.