"Congestion in the bandwidth"
Probably the funniest thing I've read all day.
Apologies if this is explaining something you already know, but "Bandwidth" is essentially the overall data rate one connection can handle. Basically how big the pipe data travels through is. Internet trunk lines can handle immense transfer speeds, but then they branch off hundreds and thousands of times to branches which splits that signal up. "Congestion" of those lines indicates they are reaching their limit because usage is very high which SLOWS DOWN everyone's speed.
How then would congestion of the lines cause YOUR data usage to skyrocket when you are using no more than you normally do?
This is a BS answer someone gave you, especially if it came from Cox.