Supersonic --- bad bad bad- stay away

I cancelled a contract with Supersonic after they took over Nepic, paid up with zero balance in 2020. Now some debt collection agency is mailing and calling me 4 years later claiming i owe money. they do not answer their phones and the debt collector tells me that i have to prove i paid up the account??? now if they (the debt collector) got my information legally why do i need to prove anything, surely Supersonic can provide all relevant details?? but seeing as they obviously bought a "so-called: debt *******ly i would steer very clear of Supersonic