Gave modem to parents can’t receive calls

i canceled optimum. yeah for me. i gave my parents my old modem (i purchased). everything works on their network except incoming calls. also when i make. call from their phone it shows my name. i tried resetting it. it still doesn’t work properly. help what do i do?

also i called to get their bill down. the guy gave me numbers which i wasn’t totally happy with. but i took it. then when he’s reading the disclosure he said the prices didn’t include taxes and fees! i flipped. he insists he told me. i told him to play back what he said that he’s deceitful and a liar. i’m sick of this company. I’ve wasted hours of my life talking to them.