What kind of pump did you have before? Shallow well or deep well jet? What is your depth to water level in the well?
It is likely that your original pump had less capacity and was drawing water from a higher point in the well. The lower flow let the sand sink to the bottom and not get in the pump.
How many GPM with the new pump? How many GPM with the old pump. What depth to the foot valve with the old pump, compared to the 75 ft to your new pump?
When you have the above information, you will probably see the reason for the problem. Post it and see if it is confirmed here.
My guess is that the new pump is farther down in the well and pumps more water. That greater flow is producing higher velocity in the nearby aquifer, sucking out sediment that your old pump would not move.
Before they put in the new pump they should have dropped in a big pump with higher flow than your new pump, and pumped until the water was clear. Then they should have put in your new pump.