CRS can be difficult to sex. With that said, I doubt that you received all males with your last shipment. How many shrimp did you receive? I am new to CRS/CBS and when I received my order I looked at them and thought I had no females (I was comparing them to my RCS females). I asked the seller if he sent me any females and he told me that he was certain that I had females. Three weeks later (four weeks after putting them in my tank) I noticed that I had a berried female CBS.
What makes you think that they are all males? Are they not breeding for you? If so, what are the water params?
What makes you think that they are all males? Are they not breeding for you? If so, what are the water params?