Licence still not cancelled

I found out today that I have been handed over to attorneys with regards to a tv licence which hasn't been paid. I cancelled that licence more than 4 years ago when my husband and I moved in together and I got rid of my TV and we use his tv which has a licence on his name. The more I tell this debt collector that its cancelled the more she argues with me and says I must prove it, everything was sent via my previous job's email address and I don't have that anymore as it was so long ago. The worst is they insist it must be paid and it doesn't matter that you cancelled or don't even have the TV anymore. ***???