Incoming call of 1 contact not ringing

there is one contact, whose incoming call is not ringing - all of a sudden. the number is NOT blocked, a ringing tone is assigned to it, and I find the calls in the Anrufliste.
all the other incoming calls work normal …
any suggestions, what to do ???

Is it a ringing tone that only this individual contact “uses”? Is this ringing tone stored on an SD card in the phone or in the phone’s internal storage?

its one of the phones tones