Handed over

I keep getting sms's to say i have been handed over and have to call these people to pay the account.<br> According to my records the account i had with Nashua Mobile has been paid up 2 or 3 years ago and did not renew the contract. They cannot give me proof of the amounts that were outstanding before 2014 , only the current statement they received from them as of 2014. When you phone the numbers they give on their site it shows as INVALID number and when you mail the addresses they show it also comes back as undeliverable. I would like to resolve this asap. If someone can help. <br> Thanks<br>