Im having hard time getting traffic. I'm running directlinking to creditreport.com. My MAX DCPM is set to $11.00 and Target CPV $11.00. This is just for testing, so my daily budget is set to $50. My campaign is running, but i'm not getting any traffic. What do I need to fix? 
What traffic source is that , self-serve or not?
If it's not self serve you should ask your rep to look into it.
Should I increase Target CPA to $20, cos offer payout is $26?
I never used them but increasing the CPA will give you a higher chance to get traffic.
Same goes with increasing the budget / frequency cap.
Also , on most banner networks you have to wait about 3-4 hours from the campaign approval to start seeing any traffic.
Once we have profitable campaign, whats the guarantee that the media buying network will not copy your campaign?
There is none, but trust me, most get the long term value of you as a customer. We've had some rip my stuff off in the past, and we stopped spending with them, and spent a lot more with the solid companies. Having worked a LOT with XA.net I can tell you they're legit...
have any rep you can recommend at xa.net?
You should look into direct media buys to be honest. Much easier to negotiate cheaper CPMs to get the "ROI" you really desire. They're are still tons of sites out there for almost every niche, just gotta dig for them!
-dub
Dont direct link with credit reports. They work good as upsells in my experience, or in addition to offers like insurance/loans/etc.
'Now that you filled out a lead form, the next step is to check your credit!' in a popunder or banner after a form fill
Checkout how http://lowermybills.com/ (a large advertiser) does this and you might get some ideas.