Owning money on an account i dont own

I received a lawyer call on behalf of nashua mobile saying i owe money for over R2000 on a nokia N8, i dont even know which phone that is...i was told i am required to pay it asap to avoid legal action. I was a customer in 2007 their service was so bad that as an apology they gave 50% off my contract for a year, i cancelled my contract years ago due this service and now this. I would like someone from nashua to call me and explain to me what is going on, and i would like this taken care of in a professional manner.