Go through your previous bank statements to get the confirmed date. The law firm is trying to manipulate the dates and give it a current look. Re-aging of accounts is illegal in FCRA
To prove yourself in the fair side, you need to prove the dates from your bank statement. It won't take long for the judge to understand your story if you have the bank statement. On this basis, you can even file a lawsuit against the CRA and the law firm for reporting inaccurate items without showing proof. You need to explain your part so that the ball rolls in their court and the burden of proof falls on Capital One or the CRA.
First, highlight this item and dispute with the Credit bureau to correct the entry. Ask for the results of investigations if they decide to continue the reporting. This must not be the case if you have your documentation complete. If this is not resolved, speak with a lawyer who deals in lawsuits of fdcpa and FCRA violations.