The Lincoln Medical Centre's main phone number is finally working again after months of relying on temporary numbers due to a Telstra processing error.
The clinic had experienced difficulties with its phone lines since at least June with patients unable to connect through the main phone number.
The clinic's main number returned to service on October 30 after the Port Lincoln Times contacted Telstra.
Practice manager Bridgette Perone said new numbers were set up to receive calls but if the line was busy, callers would get an engaged signal or be told the line was disconnected.
She said it had been stressful for patients, specialists and hospitals trying to get in touch with the clinic, as well as staff who had to field complaints from clients who could not get through.
Telstra SA regional general manager Mark Bolton said the issue appeared to have been caused by a Telstra processing error when a request was made mid-year to change the telephone service from analogue to an nbn digital service.
He said the clinic was never without an active telephone service and Telstra had apologised for the issue.
"We are also aware the centre are still experiencing a high volume of calls and are currently working with them to identify options to resolve the problem," he said.
Ms Perone said the clinic had received no correspondence directly from Telstra and had been going through a technology solutions company.
"Being a medical centre we should have been a priority to get the problem solved."
People can now contact the centre on 8682 5133.