There are multiple factors we take into consideration in these cases, style (ouline/glyph etc), colors, shapes, concepts/metaphors, while some styles and some metaphors are common these days in a lot of sets (like a truck in outline for shipping), the sets that cover all the factors above are usualy plagiarism.
Taking your icons as an example the style was filled outline, a pretty complex style, so i would say the coincidence factor here would be low. It would be fine if 1 or 2 icons were somewhat similar, we would call that a coincidence, asked you to remove, but in your sets the problems were wide spread, the more we searched the more we found, almost 1 to 1 translation of the icons, across multiple sets and covering all these factors listed above: toned outlines, pastelized colors, shapes, sizing, positioning of elements etc.
While we see the icons were done by someone else it is also clear the Icojam sets were underneath them. If you are a team leader, you should have controlled the inspiration feed of your team and outcome of the work better, while creativity starts with inspiration and sometimes even sparks from imitation, it must diverge to a degree of originality when things start being about money, otherwise these problems will always come to the surface, always.