Just musing…Based on your scenario it could be so simple as they changed your port profile because they could, or possibly because that is your plan, which you did not mention but implied it was 50/20 per the first 12 months speeds. Could it be that you inadvertently bought a plan that was ‘upgraded’ to 50/20 for a year and they dropped it back to 12/1 at the end of the original offer?
Going a bit off your problem, I’ll reference my old post for something probably unrelated but that could be helpful (or not) to others.
Some FTTN modem-routers might also have an SNR setting. Check the manual. If you are not getting the speeds you expect experiment with it. It might not be documented but could be worth a google search to see if it has been ‘discovered’ or is not supported as a configurable setting in the product.
Also, it is my understanding that ADSL/VDSL copper ports have profiles at the ISP/RSP end that are configured for stability or to a policy. Sometimes a friendly tech can be persuaded to set a particular line to ‘performance’ but they don’t easily do it because their end will also run hotter, use more power, and they have their directives. All that is secondary to the plan, and that will limit the max regardless of whatever else is ‘in the way’.
