My stepdaughter is on Skinny. The answer phone service on her Iphone 11 had been working fine untill now. 

Some people phone her and if she doesn't answer the phone just keeps on ringing and will not activate the answer phone. For other people the answer phone works. She has talked to Skinny and they say her answer phone is setup fine on there end. They have also sent a new sim which didn't solve the proble. Anyone have any hints or suggestions?