cellc contract cancelled but never cancelled bill

my husband had a contract over 3 years agoe with cellc we cancelled the contract due them always double debiting us, we eventually got tired of trying to rectify the accounts and we cancelled the contract, returned the device and cellc cancelled the sim card, after 3 years cellc hand us over for money outstanding from this cancelled contract yet they where at fault and had no decency to contact us to say if there is outstanding money and if there was we need to pay it. Now 3 years later they hand us over, i need proof of how much was outstanding on the contract, as i refuse to pay for a handset we no longer have neither a contract, cell messed us around and i have seeked legal advise and i will forward all costs to cellc, as they cellc is trying to make easy money from us.