Sales tax can’t be charged on internet service. One company’s making a big mistake.

Maria Markovich keeps an eye on her expenses.

Rather than use a big-name carrier for internet service, she uses a Brightspeed, a discount provider, for her Hunterdon County home.

She no longer has a landline or a fax line — they were rarely used so she dumped them to save a few bucks — so her bill for only internet service was $55 a month.

All was well until her September, when her bill was $3.64 more than usual.

Suddenly — and for the first time — Brightspeed was charging sales tax on the service.

Markovich remembered that internet service is exempt from sales tax, so she called customer service.

“When I finally got through to a person, she seemed to be reading from a script which said, `fees and taxes can increase any time,’ which she repeated no matter what I said about the exempt