debieecakes,
The fact that you were able to stream Netflix in the past after you had run out of data, and without purchasing tokens or being in the Bonus Bytes period, is frankly amazing.
The throttled speed when one runs out of data is around 150Kbps, which is pretty much what you are getting. Why you were able to stream Netflix after running out of data before is a complete mystery, at least to me. Even on Low Def I don't think 150Kbps would normally be enough.
Some plans have a thing called Smart Browsing, and that's so people can still browse without seeing any noticeable difference when they are out of data, but it's not geared toward data intensive things like streaming and will generally not work with such. It sounds like your plan may have this, though when the system senses that there is a sustained high data activity occurring the Smart Browsing basically turns off and you are again throttled to around 150Kbps.
When you run speed tests while in smart browsing, depending on how large the speed test is, it could show you a decent speed or a throttled speed, but again, Smart Browsing isn't geared toward streaming, only general browsing.
The only solution to your issue is to either be more conservative with your data usage or purchase tokens.
If you stream on a regular basis, that would explain where all of your data is going. But, if you don't stream on a regular basis, we need to find out why all of your data is being used up so quickly, as 50GB is a HUGE amount of data to use when not streaming regularly.
Again, why you were able to stream in the past when you were out of data is a complete mystery to me, but it generally doesn't work.