And it will be another four days before they are fully reconnected.
Several businesses in Hidden Lane off Argyle Street – including a funeral parlour, a doctor's surgery and a magazine – are being affected.
The firms have been given one line each, which they say isn't enough.
Publisher Susan Young, 47, of Fenwick, is organising the Pub of the Year Awards, which are to announce their results next week.
She said: "We simply cannot operate using only one line. Half my staff can't work. We have journalists trying to get stories and salespeople trying to sell advertising. Lots of calls are being missed."
She has called BT every day for the past few weeks. At first she says she was told the fault lay with Glasgow City Council, but they passed her back to BT.
Ms Young added: "BT are only paying lip service to our complaints. The people we have spoken to have been pleasant, but ineffectual."
As a public utility firm, BT is allowed to dig up roads, but only have to notify council, rather than seek permission.
A spokesman for BT apologised. He added: "We suspect this cable has been damaged by contractors excavating at the entrance to 1103 Argyle Street.
"We are working to restore service but the cable duct across Argyle Street is blocked and attempts to clear it have failed.
"The cable runs under Argyle Street which is an extremely traffic sensitive location and work is only permitted out of hours.
"Our contractors are to return to the site to lay new duct on Monday night and the early hours of Tuesday. Ms Young's incoming calls have been diverted to her mobile free of charge."