Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, bear with us; re-confirm and post back with the complete model number of the phone system. Additionally, who is your phone service provider please?
Appreciate the additional information.
It may not be an issue with your phone nor service provider but most likely with that of the party calling. Can that person call any other number successfully?
AT&T has a "Call Block" feature. Has this been engaged/enabled at your end?
I understand; still, can you please try dialing * 8 0 and listen post back with any operator message?
Other than number/call blocking, there is no other feature that your phone nor your phone service provider would restrict only a specific incoming number.
Have you tried bringing this matter to the attention of AT&T at 1(###) ###-####
Yes of course and would look forward to an update by tomorrow or when able.