These satellites are hundreds of miles from each other. Furthermore they are in LEO which means the orbit decays in under 5 years if they don't have regular thrust correction. We've already had satellite collisions in space and last I checked space is still fine. The only way for Kessler to be real (and that too temporary) is if someone put hundreds or thousands of tons of ball bearings above a certain size up there.
Well, Kessler's orbital mechanics work out. Objects travelling over 28,200 kpm have incredible kinetic energy. A space shuttle window was very damaged by a paint fleck. There results of larger object collisions will be all that much more impactful - pun intended. That transfer of energy will send some of the debris higher., some lower.
Just recently, the Shenzhou-20 was damaged by space junk. https://www.scientificamerican...
An Intelsat broke up in orbit recently. They are still investigating the cause. They are now tracking an increasing number of objects from the explosion. https://www.space.com/intelsat...
And since it is becoming pretty difficult to insure satellites now, a lot of sats are launched without insurance, and the companies are making them as cheap as possible. They aren't as robust, since losses will be uncompensated. https://www.space.com/space-ex...
Finally, if you want to see destruction, a country that can achieve orbit could place a bag of sand or ball bearings in a retrograde orbit, and bring the whole house of cards down as the exchange of energy and subsequent destruction occur.
Even that best case scenario of 5 years for the carnage to de-orbit, I'm not sure that people will want to wait that long to get their internet.