Is the phone's base station connected directly to a telephone line or to an internet modem connection for a voice over internet phone service?
If connected to a telephone line, disconnect (unplug) everything that is connected to the telephone line (check if more than 1 phone line socket in the premises) and then use another phone e.g. mobile phone, to call your landline phone number.
If you get a busy signal then the line is faulty. Contact your landline service provider about the problem. Tell them what you just tried.
If you get a ringtone signal, then use a screw driver (or even a pair of scissors) to short out the two wires in the telephone cable socket where the telephone's base station was plugged into to see if you can "trip" the ring signal i.e. make it stop ringing in the mobile phone.
If it doesn't stop when you try this then there's a problem on the line. Contact your landline service provider about the problem. Tell them what you just tried.
If it stops when you try this, then most probably there's a problem in the telephone's base station or the cable between the telephone cable socket and the base station.
If connected to a modem, try resetting the modem by disconnecting the power to the modem or turning it off (some modems have a power on/off switch on the back somewhere) for about 2 minutes and then turning it back on again. Allow the modem time to fully initialize and then check if the phone service is working.
If it still doesn't work, contact your internet service provider about the problem.