DALLAS -- A bank robbery in progress usually brings a quick police response, but not if the callers can’t even get through to 911 and are being placed on hold.

Witnesses to a robbery in progress at a Chase Bank in North Dallas couldn’t get through to 911. According to police records obtained by WFAA, eventually someone called the North Central Patrol Station to alert them of the robbery 15 minutes after it happened.

”It’s very frustrating, but I just hope they fix the problem,” said robbery victim Sonja McCalister.

WFAA told you about the issue a month ago after McCalister’s car was shot, and she too couldn’t get through. We went back to talk to her Monday afternoon.

”I called 911 and no response. They put me on hold. I called like seven to eight times. On hold," she said.

As WFAA first reported, the problem is with T-Mobile. Dallas police say when a T-Mobile customer calls 911, their phone keeps dialing the system multiple times.

The calls come through as hang-up calls, so 911 operators have to call all of those numbers back to make sure someone isn’t in distress. That is bogging down the system.

”I just think they need to fix the 911 calls, or someone is just really going to die if they don’t fix the problem," McCalister said.

Multiple sources say that at one point on Friday night there were 180 calls holding. Police officers on special assignment had to help 911 operators call people back.

All of this is draining DPD resources and putting citizens at risk.

Dallas police say T-Mobile engineers have been working on a solution, but so far nothing has worked.

DPD has filed a formal complaint with the Federal Communications Commission.