who owns my SB6183

I have the SB6183 and have had it for at least 10 years. I swear I bought it from my ISP (Suddenlink, now Optimum-they suck) instead of renting. I never rent service equipment because it’s soooooo much cheaper to purchase and own. Otherwise, it has to be returned when you cancel service, even if it’s obsolete after a certain time period. Plus, at the time I chose to buy it rather than rent monthly, circa 2015, it was the best available. But I have no record to prove I own it and I’m getting harassed by Optimum that even though I properly canceled my service, following their online protocol to a T, that I owe them money, 10 months after I switched ISPs. They have sent me to a debt collection service at this point. I need to find out if the serial number is registered to an ISP as their equipment they rented (in which case I lose) or if I actually own it. I would have had paper records 15 years ago, but no longer. For me, it’s not about the money, it’s about the principle of the thing, and how company es like this think they can bully the average consumer and threaten your credit, so most people just pay up. That makes me want to fight even more. How can I research this particular modem to see what the ownership status is?