I actually had a margin call on one of my TDA accounts. I was fully invested and did not have the $38 cash to cover this fee. I tried to sell a bit of a couple of other things, but the sell orders would not go through. I messaged them. A couple of days later, they messaged me back that they would refund the fee, but they didn't see where there we any sell orders. They suggested that I may have messed up putting in the orders. Its possible.
I messaged them back telling them that I have a few shares in another account and was charged the fee in that one too. Haven't heard back from them.