TelstraClear has apologised for accidentally overcharging TXT-a-park customers.
"A billing error has today been identified where TelstraClear mobile customers using the TXT-a-park service have been over-charged GST," the company said in a statement today.
"All customers charged extra GST will have their accounts credited any overcharged amount before their next billing cycle."
Spokesman Steve Jackson said customers would also get a $25 goodwill credit.
"We were alerted to the potential problem yesterday, and worked overnight to identify it. We're grateful to the customer who raised it.
"Again, we apologise to our customers for the mistake."
3 News