I've used Mirtazipine before, and it did help with anxiety as long as the dose was kept high enough. Low doses just don't cut it.
I've also heard some reports that Tianeptine Sulfate can help with anxiety. I have tried this out too and it was very effective, but I had to discontinue use as it made me very drowsy. It is easily and cheaply available on the internet, but it is also very addictive and the withdrawals are apparently hell, so it would have to be used with care. If you're interested, there are reports on it here on Bluelight and also elsewhere on the internet.
Some people have found kratom an effective remedy for anxiety, it is also useful for smoothing out the worst effects of withdrawals when tapering down from opiates, but some benzo users have found it very helpful too. Again, there is a ton of information on it here on Bluelight. Again, it is addictive, but tapering off kratom is a breeze compared to tapering off opiates or benzos.
I wish you all the best in your quest and hope you will find both useful information and support here on Bluelight.