Unable to call a specific number with my AT&T landline cordless phone.

I am currently using an AT&T cordless phone model#CL82229 IDTE S/N 4H601144967. As of Dec. 1, 2022, I have not been able to dial my neices number with either one of my cordless phones. The call will ring once and go straight into voice mail. She called her carrier T-Mobile and they did a trouble-shoot and found nothing, my number is not blocked on her end, and I also contacted my carrier Frontier Communications and they also troubleshoot my phone lines, the technician advised me that the problem is with the phone itself. I cannot find a feature on this phone that might help me to alleviate this problem, is there anything I can do besides buying a new phone, which is now very very expensive for me; being a senior citizen on a fixed income? I still prefer to have a landline because it is more convenient for me not having to worry about the dropped call in the middle of important conversations.