S2721Q, won't fit in MDA20, #2

I'm having this exact same issue too. My S2721Q will not attach onto the MDA20 for some odd reason. It appears that this issue is common with others online. When I try, the top part fits, but when getting the bottom prongs to fit, the top protrudes. Unfortunately, I had purchased these products used/second hand so I don't think Dell will bother to help me out. Well this really stinks!