Greg Mason does not dispute the money is owed, but said Contact was partly to blame for the situation.
He learnt of the debt last week, having reconnected power in his name to the Barton St, Brockville house which his sister rented.
Mr Mason said when he reconnected power to the house, Contact told him there were ''outstanding payments'', but not how much was owed.
He said a Contact employee called him on July 5 to say $11,589.79 was owed, and to make arrangements for settling the account.
''I laughed at first. I couldn't believe it,'' he said.
Since then, Contact had told Mr Mason he was only liable for power used after putting the account in his name, not his sister's debt which still has to be settled.
Mr Mason said his sister moved into the house and had power connected with Contact on April 29, 2010.
She lived at the address until December last year when she moved to Christchurch but kept paying rent on the Brockville house, he said.
No-one else was living in the house and power was disconnected on December 7 last year, Mr Mason said.
He recently decided to move in with his sister, upon her return to Dunedin, and so had power to the address reconnected.
Mr Mason said he knew people who had their electricity disconnected after failing to settle much smaller accounts, and he could not understand why Contact had allowed his sister's account to get so out of hand.
''My mate got a disconnection notice for owing $16 after a month,'' he said.
A Contact spokesman said details of individual accounts were not discussed publicly to protect the privacy of customers, and the situation at the Brockville property was ''not straightforward''.
''We have been regularly engaging with the current occupant to work through the details and an approach to paying for the historic energy consumption which has not been paid for,'' he said.
The spokesman said when a customer's debt continued to increase, or no payments were made, the company disconnected power ''as a last resort'', working within industry guidelines.
''To avoid surprises, it is important that when consumers move into a property they sign up with an energy retailer so that consumption of energy can be billed on a regular basis. Once a consumer does sign up with Contact, we are able to both bill regularly for energy usage and also identify customers who are having difficulty paying their bill or have an increasing debt with Contact early on, to enable us to work with them and explore options and hopefully rectify the situation.''
The company would not elaborate on the Dunedin case.
Electricity consumer advocate Molly Melhuish, of Wellington, said both parties had responsibilities in respect of accounts.
Contact and other electricity retailers were encouraged to do everything they could to help consumers pay bills, in some cases by referring them to social agencies like Work and Income or contacting relatives, Mrs Melhuish said.
''Guidelines require the retailer to take active steps to approach consumers who have had late payment notices, and discuss payment alternatives. If Contact has been proactive, then you can start pointing the finger at the consumer.
''Otherwise, her brother is quite right. Contact should not have let the arrears get so out of hand,'' Mrs Melhuish said.
Acting Electricity and Gas Complaints Commissioner Nanette Moreau said Electricity Authority guidelines included an onus on retailers to identify problems and try to rectify them with consumers as soon as possible.
There were specific expectations on retailers in respect of vulnerable consumers, including those who could not pay bills or were medically-dependent, she said.
Ms Moreau said retailers did not have an obligation to supply power to individual consumers and it was not in companies' best interests for debt to mount.
