It's not an open, and it's not a short. A toner is not the tool to use to test a line.
Open the line at the demarck. Draw dial tone with a known, good test set or single-line phone that does not require a separate power source to operate. Listen to the line after dialing a digit.
If the line sounds good, proceed to the next step.
With the line open at the demarc AND ALL EQUIPMENT REMOVED FROM THE LINE test with a meter for grounds and crosses.
Put the line back to normal and listen with JUST the test set or common phone at the end location.
You have a ground, a cross, an unbalance, or a defective telephone.
