why sometimes I'm banned and sometimes not

I'm opening plenty adwords accounts(I have nice pack of vouchers). And I noticed something weird. I'm opening account, set up test campaign and everything works fine. Add second campaing and sometimes ban and sometimes not. Using this same keywords on this same domain or different domain it doesn't matter. IP, cookies what else? I'm using proxy to get different IP's. Maybe problem is that I have billing adress in one country and I'm conecting thru another? I was thinking that I set my budget, too high. But that isn't it. Or maybe I should run test campaing for couple of days and go back to it?

Get a proxy with right geoip, non blacklisted and which does not look like a proxy (hostname)
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I'm using your service from few days But I still see these same fast proxies or I have to choose something slow ... or in different country than US. If I want us proxy that is real disaster. When I choose proxy with speed below 7/10 It's takes a lot of time to create account. Probably I'm doing something wrong Sometimes 9/10 proxy doesn't respond or is slow I don't get it why. How can I know that proxy is banned ? I'm not using proxy with suspicious hostnames.

Once you get banned by adwords, really banned they hit you hard-core. I got banned with like 15 accounts a few years ago. They got every account associated with the same ip addresses, and all credit cards. My credit cards are still no good for adwords now. The billing address can't be the same either. Nothing in the account can be the same as banned accounts. If you get banned look at the credit card as one of the main things they look at, but definitely ip addresses. If you use gmail then that can screw you also because your ip for gmail get's associated. You have to use a proxy and new cards every time from then on.