Capital 95.8 have re-started a competition worth 155,000 pounds, despite the prize been won a fortnight ago.
The original winner has been deemed ineligible by the station. Capital have referred the details of regulator Ofcom, who are looking into the matter.
The iTest competition requires listeners to register and then guess the identities of three celebrities, only by them saying the letter I.
Two celebrity voices had been guessed; the third correct guess meant the listener won the accumulated prize money, which stood at 155,000 pounds.
According to a statement on the Capital 95.8 website: "Immediately after any competition is won, Capital checks that the winner was eligible to take part in the competition and that prizes have been won fairly and in accordance with the terms and conditions of the competition."
"In this case the caller was not eligible to win."
According to the Guardian, a spokeswoman for Ofcom confirmed the regulator was considering the details of the competition but was not making a formal investigation, as no listener complaint had been received.