No, they could not, because laws are interpreted so that every word must have a meaning, and if "impose conditions" could include "the condition of 0 kb/s" it what have no different meaning then "terminate" and that would violate the cannons of statutory interpretation.
They also could not because the charter would prohibit it. While not all speech is protected by the charter (your categories aren't the right one, but there are categories like CSAM and hate speech), the government doesn't have the ability to prevent significant amounts of protected speech to prevent unprotected speech without invoking the notwithstanding clause (which this law does not).
You're right, 0 kb/s would be too obvious. Let's do 0.1 kb/s, or restrict their plan to 1 minute of use per day.
You realize that while the charter still safeguards your freedoms, it will eventually be overturned if the populace gets used to more and more control over time. Laws like this are cracks in the dam. If you pay no attention to it or give it charitable interpretations, then someday the dam will crumble.
They also could not because the charter would prohibit it. While not all speech is protected by the charter (your categories aren't the right one, but there are categories like CSAM and hate speech), the government doesn't have the ability to prevent significant amounts of protected speech to prevent unprotected speech without invoking the notwithstanding clause (which this law does not).