Phone lines not working on weekends

Hello,

I've noticed an unusual issue with our phone lines. From Monday to Friday, they operate without any problems. However, on Saturdays and Sundays, there's a complete silence when calls are made to our lines. There's no ringing, no sound from the dialer, absolutely nothing.

Interestingly, texts sent to the phone line are working fine.

Could you provide some guidance on how to resolve this?

Thank you.