canceled contract 10 years ago still gets demands

me and my wife took out a contract each 3 months before contract expired i canceled it as required with filling in cancellation form and e mailing it to Nashua mobile i stay at the same address for 12 years 4 months ago my wife got a demand she ow them R 250 she paid it for arguments sake Now they demand R 2400 from me but we had the same contract and it was canceled on the same day