Old charge off coming up again!

I had a credit card that got charged off originally about 12 years ago. The total balance then was well under $1000. Then about 3 years ago I got pegged by one of these bottom feeders. I believed them when they told me that I was going to be charged with fraud, gave them my bank account info, and ended up paying them over 1800 bucks. Of course I got no paper work stating that the debt was paid off, and now another company is after me, using the same tactics. I'm a little bit smarter now, (but not much), so I told them over the phone to send me a DV, and have heard nothing from them in a week. The SoL in my state is 3 years, and we are right at that mark since I last paid the other company. Should I send them a certified letter, or should I just let the clock keep ticking for a while? These folks said the balance is over $4000. I have no interest in sending a penny to any more of these jerks. Thanks for any input!