Just to follow-up on the C1-PLL. The filter is built into the hardware. If looking at a spectrum analyzer you would see the RF cut off at 3.6GHZ and soft slope above.
Need to determine if the RF is getting into the cable drops or via the reflector/feedhorn. Would be easy to see if you had a spectrum analyzer, but we can investigate a few other ways.
Are the coax lines close to each other? It might be easy to run another drop out to your satellite system at a distance from the internet drop. If this fixes the problem, and the drops must be run close to each other, snake one cable over the other in a repeating "S" pattern for the length of the run. This may cancel out interference between the two drops.
As an experiment, just have someone get close behind the WiFi antenna between the WiFi and the dish. This might show if RF blocking will keep the WiFi signals from getting into the feedhorn.
Could you temporarily move the WiFi antenna to an area behind your dish or better yet around a corner use the building to shield the dish from the WiFi antenna?
We used to erect chicken wire fences to shield C-band dishes from terrestrial interference, like point to point telephone links or radar from local airports. If the WiFi antenna cannot be moved, try building an "RF Fence" behind the WiFi, between the WiFi and the dish. A single layer of chicken wire fence material attached to metal fence posts or to a ground rod if using wood posts.