Since you can get 300 Mbps wired, then we can likely eliminate your ISP or their equipment as the source of the problem. So the root of your issue appears to be the wireless aspect of your router. Either the router doesn’t support wireless throughput that high, your devices don’t support wireless that fast, or your router is malfunctioning. Without more details I can’t exactly answer that question, but if you can respond let me know what kind of router you have and which devices you are testing with. I might be able to tell if your routers and/or devices can support fast enough wireless to get 300 Mbps throughput. That being said, if you can get 200 Mbps wireless, that is pretty fast!