DSL speed decreased suddenly

I have an Internet 12 DSL plan and over the past 10 days the download speeds for my connection seem to have suddenly dropped to less than half of normal. Speed tests show that I am getting about 11 Mb down and 1 Mb up. I know this is in the range for my plan, but the speed of actual downloads is never what I used to get. I regularly got speeds between 9 and 10 Mb when downloading a file from various different places, such as file hosts like Uploaded.net or Zippyshare. Now I am lucky to get 3 Mb down. Has something changed?

I am on a new HP desktop with Windows 10 OS

Here are a few things I already tried to do to fix the issue - 

Reset my modem

Called AT&T for to test and/or reset my modem - the modem is an AT&T 5031NV model

Checked for adaptor updates

Tried using various different DNS settings to use public serves like 8.8.8.8 and 1.1.1.1

Set my DNS server option to use my specific server listed for my modem

Opened a new user in Win 10 and tried to use an old system restore point to go back to any older settings that may have changed because of an update.

I have used multiple browsers to see if the speed was different. Same issue on Firefox, Edge, Chrome and IE.

Any suggestions on why my speed has collapsed and how to fix it?