Perhaps you didn’t have enough max payout as their condition or you refer yourself to buy domain names?
The problem is not payouts. The problem is they are not even showing reports of clicks, conversions and sales. When I asked the affiliate manager, he said that he have no idea. I asked him to connect me to their head, but that person was also same.. he told me that I did not made any sales ( mean my referred customers). But in fact, my client have more than 20 domains with them, from the day I referred him. So I did not got anything for referring him, atleast the firstime fee also 
This is insane. Some people may not believe this, but this is real and happened with me. Thats the day I realised that never refer or recommend any third party service and I left domain buying to customers themselves. After all no one listens no matter you bang head to wall. They do what they want to do at the end of the day.
How many domain names are you having at namecheap?
Zero.. I hate them. I will give only one chance to anyone, if they prove bad, done. its over… I no longer recommend them to anyone no matter they have better UI or anything. Making someone fools is worse..
Yes, compared to Godaddy, namecheap is lot better. Still I do not like them , because they cheated me… Hope they are good atleast for you.
Another thing, one of our client purchased their VPS, despite of our warning that their server are not so good. What happend, their VPS runs dead slow, even our shared hosting is 1000 times better. Of course the clients business also collapsed… lol.. mad clients.. Even when we say for their own good, they are like mad never listen. So the lesson..never preach anyone what to do, we cannot save people who are jumping into volcano…ha ha.