A long story shortened: I, too, found out that my DNA was different than a known 1st cousin on my paternal side. We weren't related at all. My results also showed a 2nd cousin that I didn't know. This new cousin was willing to work together (that helped a lot!). I had heard rumors that my brother had a different father (I had 3 siblings-all have died now). So, I had that brother's daughter tested, and my sister's son tested. The results showed my brother and I had the same father but my sister had a different one. So, I used the rumors, which can be true, to start the search along with the newly found cousin. Together, we were able to pin it down. I contacted one of the family members of the father I thought was now mine. She took a DNA test and voila! We were related. So, there are ways. Some are through rumors, new connections, and the willingness of people to give samples. I hope this helps you some.