It seems there are still some glitches with the STM's smart card.

Some transit users have been charged twice for their monthly OPUS pass, while others were charged even though their transactions didn't go through.

When Alex Harper tried to top up his OPUS card at a machine recently, he ran into trouble.

"I tried to refill my OPUS card and just as the transaction was nearing completion, both screens gave me different error messages. One told me the service was temporarily unavailable, and a second told me that no transaction had been debited," Harper said.

But according to his bank statements, he was charged $68.50 for the monthly pass -- which he was unable to use.

Harper contacted the STM and explained the situation.

"They reassured me I would be refunded," he said, adding that he hasn't received any compensation so far.

Another transit user, Justin Stuart, also had problems with an STM smart card machine -- he ended up being charged twice for his July pass.

"I understand that these things happen. It's normal. Glitches do happen, especially with a new technology. I just want them (the STM) to admit their mistakes," said Stuart.

The STM told CTV News their lawyers are handling the complaints, and if anyone has any issues, they can call customer service.

Harper said he finds the situation frustrating.

"They raise their prices, we pay. The buses are late, we wait. The bus doesn't show up, we wait for the next one. All I ever wanted was service I can count on."