I had similar situation couple of times - too big transaction that was rejected by network.
( ~3 mln as I remember, - only 0.3 btc now)
Polo has to reset their wallet, but their support is very slow. You can wait for this for weeks or even monthes

Maybe such cases is the reason why they want to remove XDN

Anyway, I remember that SJCX withdrawals were pain in the ass too, so I dumped it below 3000 sat.
And after this it was pumped hard