Hey there @Sailor01 and welcome to the Community!
There could be a lot of reasons why you may experience slow speed and that can range from your physical location to hardware issue to software issue and to network congestion.
That said, to answer your question, we do not throttle down your speed when you are late in your payments.
Here is another similar thread you might want to take a few moment to read as it could help you a bit with your situation.
Hope that helps!