We now need to do some isolation testing to figure out where the problem lies.
At this part of the troubleshooting flow, we need to try a different phone to ensure the problem doesn't lie with your handset. Check around your home and see if you have any old phone you can use. Simply plug it into the port your phone is currently plugged into and re-test. Don't forget to plug in the power if your phone requires it!
Has this resolved your issue?