Direct Drive VS Belt Drive

You have not provided enough information for a complete answer, only conjecture. But we can deduce the most likely possibility and address the "legal" battle you are experiencing here. It's not about your having violated any of the puny laws of humans, it's about you not understanding the immutable laws of physics, namely the First Law of Thermodynamics and then Affinity Law 1c.

Your first offense is that of hubris against the First Law of Thermodynamics, which partially states that energy cannot be created or destroyed, only transferred. You were attempting to do the same work using less energy in a system, namely, changing components and expecting that magically, energy would be reduced. This law says that this can NEVER happen, at least by magic. The closest we mere mortals can come is to first IDENTIFY someplace in a system where energy is being WASTED, then removing that waste in a method that does not sacrifice performance of the system. You may have assumed there was a lot of waste in the belt drives, but obviously did not fully understand the system first, you simply removed belt drive components without fully understanding their function, expecting that magically, this would reduce the energy. It's never that simplistic.

Next, you paid no heed to Affinity Law 1c, stating that in a centrifugal (quadratic) machine such as an air fan, the power REQUIRED by the machine varies at the cube of the speed change. This is where we must deduce your error by virtue of your complaint, because in complaining of the motor overloading, we can deduce that your belt drive system was DECREASING the fan speed compared to the motor shaft speed. So by eliminating that reduction ratio, you INCREASED the speed of the fan blades themselves, thus increasing the power demand from the fan by a cubed factor. As an example, let's say you had even a modest belt reduction ration of 2:3 meaning that for every 3 motor shaft rotations, the fan shaft rotated only 2 times. Expressed fractionally, the fan turned at 2/3 the motor speed, or digitally, .67 times. By directly driving the fan, the speed increased by the inverse of that, so now your fan would be spinning at 1/.67 of what it was, which is is 1.4925..., so roughly 150% of what it was spinning. Now, as per Affinity Law 1c, the fan will DEMAND 1.5 x 1.5 x 1.5 the amount of power from that motor. So now let's pretend you originally needed 90kw of mechanical power for the belt driven fan, so you had a 100kW motor driving it with belts to reduce the speed. By removing the belts and directly coupling it, this meant increasing the fan speed by just 50%, which then means the Load REQUIRED by that fan increased to 1.5 CUBED, or 337.5%, meaning the motor needed to be at least 303kW! 100kW motor connected to a 303kW liad = failure...

Now, physics does allow for adjustment in flow to lower the power requirement, stating that the power required by a fan reduces as the flow reduces. But to accomplish this with that same example speed change, you would need to restrict flow drastically, and at the same time suffer consequences of increased static duct pressure that may end up blowing out your air ducting seams.

In theory, you could add a Variable Frequency Drive to that motor and reduce the motor speed again, but here too, it's not that simplistic. In addition to reducing the SPEED of your fan, the belt drive system also INCREASED the shaft TORQUE at the fan. When you use a VFD to reduce speed, you get, at best, the SAME torque at the lower speed. So unless the fan did not really NEED that added torque at the reduced speed, this too could result in failure. Generally, when a fan manufacturer picks a motor size to operate a fan that uses a belt drive to reduce the speed, they will put in the minimum size motor they can use, base UPON the shaft torque the fan needs. In other words it's far far more likely that your fan will need the torque provided by the belt drive at its shaft, meaning your motor might still be too small even with VFD reducing the speed.

We the jury of your peers hereby sentence you to 30 weeks of studying physics as it relates to air handling systems.