Thousands of mobile phone customers have been left out of pocket after signing up for a cashback deal with a Birmingham-based company.
The shutters were down at the shop in Bordesley Green
Trading Standards officers are probing Mobile Communications, now known as Dialamobile, which has closed its shop in Bordesley Green.
Hundreds of angry customers have travelled to the store, where a sign advises them to call Trading Standards.
Trading Standards said it had taken more than 400 calls about the company.
Customers had signed contracts at the store with one of the major mobile phone providers.
The provider then charged the customer a monthly line rental and paid the store commission.
But customers say the store promised to reimburse customers' line rental costs for a year, but the payments have stopped, leaving customers tied into contracts.
One customer, Millat Mustafa, said: "I'm really, really frustrated and really, really angry with the service they've been providing. I'm really distressed."
Chris Neville, of Birmingham Trading Standards, said: "We've seen many examples of retailers who've got into exactly this position.
"They find that they can't fund cash back deals and then they disappear.
"It just leaves lots of customers with very expensive phone contracts that they didn't expect to end up with."
No-one from the company was available for comment.