A few days ago I sent out all of my XST from my Ledger, the transaction never went trough, blockexplorer tells me, that my coins are still in my wallet but my ledger wallet shows me 0 XST

This is the transaction:
https://chainz.cryptoid.info/xst/tx.dws?b71b9e1d5623f62733e98b8118d96df31a0465c13fd608c9332ce26420feaa37.htm

note the date! 1899-12-30

And now my ledger only shows the incoming transactions, no outgoing anymore, balance is still 0 XST.

so your method does not work for me.