Me too, when I was still actively gambling at duelbits, I used VPN most of the time. I did not win big too, my biggest withdrawal from duelbits was around $3000 and there was no issue at all.
Ooo still a pretty good amount nevertheless. May I ask if you were using a dedicated IP or was it simply a regular paid VPN? I've never gambled in duelbits yet but I'm guessing they're VPN friendly?
Just a regular paid VPN, what I used to do is using Indonesian IP which is where I come from. Since I have never experienced any issue when I was active at duelbits, yes I can say they are VPN friendly but I'm not sure about now because I have been inactive for a while. You can always ask support about it if there is no written terms about VPN usage (not only at duelbits but in all casinos).