There are two things going on here.
Can you ask for a reduction in fees if your streaming service is reducing the bit rate? The answer is, yes. You can always ask. They might say no.
The next question is, can you demand a reduction in fees as compensation for a lower bit rate? This depends on what your agreement with the streaming service says. I’ve never read a user agreement in my life. But if a certain bit rate is guaranteed in the agreement, then you can demand compensation for their inability to keep to their obligations. If they refuse, you can take them to court and you will then be able to demonstrate what harm you suffered because of this.