Hi, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.
Initially, would the HP Officejet Pro 6830 print, scan and copy as expected?
Would the FAX issue be when sending? ...or when receiving? ...or both?
And is it connected to a regular 2-wire phone line? ...or through a VoIP system? ...or through an Internet service and/or is bundled with a DSL subscription?
Still, if the HP Officejet Pro 6830 can print, scan and copy as expected, then the issue would most likely be with the telephone connection and/or the quality of the telephone line/service.
Please have these checked by the phone company.