It is the wrong DSL service type. Typically this happens when trying to connect an ADSL modem onto a VDSL service.
During the installation process, you connected the phone line into a DSL splitter or filter. Do not use a splitter or filter on the phone line from the DSL wall jack to the modem as it removes DSL signal. Do not use any phone cables longer than 10 ft due to attenuation.
The DSL signal is not strong enough or too high for the modem to train/synch with the service. This needs to be corrected by the DSL provider. There may also be low or high pass filters that have been put on the line by the DSL installer that connected when connecting the service.
It is a very slim possibility that the DSL sensor on the modem is defective and the modem needs to be replaced.