having trouble sending imessages and calls to one phone number

i haven’t been able to send imessages, make outgoing calls or facetimes to my moms iphone. she does not receive any text that have been sent as sms. when i try to facetime her it says facetime failed. when she facetimes me it lets me answer then never connects and says facetime failed. every time i make an outgoing call to her it goes straight to voice mail. i am able to answer incoming calls from her. HELP, it is only happening to my mom number. i have no issue reaching anyone else.