Sorry you are not feeling well - please rest up as much as you need, and I hope you feel better soon.
But let me send a recommend RESET procedure for that modem - which often corrects issues like this.
Also, if the reset does not improve this situation, you may want to contact Optimum Technical Support, for further troubleshooting and to find out if there are any OTHER FEATURES that might be active for the phone service (such as "Do Not Disturb" or "Call Forwarding").
To do that reset, simply find the POWER PLUG in the back of that box and disconnect it. And leave it disconnected for AT LEAST TWO MINUTES, and check that all the lights are out on the front of the box.
NOTE: If the modem has an internal "backup battery", that will need to be disconnected too - so that the lights go OUT.
Then, after the TWO MINUTES, reconnect the power plug (and battery if needed), and watch the lights on the front of the box for a minute or so, as the device restarts. When the lights "stabilize", then you should be able to make a NEW TEST CALL (to or from your cell), and see if the results have changed.
Please give this reset a try - when you feel up to it - and let me know if that corrects the issue.
Take Good Care, Greg A.