Worked my butt off to get rid of PMI on mortgage, got to 20 percent paid down, and got denied. Can someone help me understand why?

Apparently the valuation of my house went down, which I call BS on, but anyway, now mortgage company is asking for another lump sum payment of thousands of dollars to remove PMI. If the valuation went down, don’t I have more than 20 percent equity?

Edit: thanks all for the tremendous amount feedback and advice, now it makes sense to me!