Retailers in and around Manchester were left without phone access after a fire in a BT tunnel severed cables.
Following the blaze, which happened the weekend before last, more than 130,000 people and businesses lost phone contact, many for several days.
Some retailers were unable to authenticate credit cards.
At the end of last week, John Lewis's Cheadle store was still battling to restore internal telephone links. However, the retailer claimed business was good. Much of the city centre was closed to allow fire brigade access, meaning that those outlets still open were popular.
A spokeswoman said: 'Our contingency plans worked well.' John Lewis is seeking reassurance from BT that such problems will not reoccur.
Manchester Chamber of Commerce chief executive Angie Robinson said: 'We put the cost of the disruption to have been somewhere in the region of£4.5 million per day.
'Retailers were having difficulties accepting credit card payments because of a failure of machines that rely on a dial-up connection.'