Telecom is refunding 150,000 customers who may have been overcharged or had their broadband internet access slowed, due to a system fault in November.
The company says it was not aware of the problem in its usage meter system until December, and by then many customers had already been overcharged or had their internet speed cut.
It says it will refund anyone who was charged for exceeding their internet use limit druing that period, and compensate those who had their access slowed.
It has also written to 150,000 broadband customers to offer to double their data downloading allowance until 15 January.
