[ca, Usa] Former Employee Sent Me To Collections Over “commissions Overpayment”

Hey Reddit. Seeking advice from some group experts here regarding labor/employment laws in CA.

So a big corporation company that I worked at for over 12 years before I resigned last year just sent me a letter last month demanding I pay them back $200 in “overpaid commissions.” I have not been employed by them in over 6 months before this letter was sent to me. They claim they paid me for a sale that they shouldn’t have. When I asked for proof, they sent me some documents that are hard to review and doesn’t really show whether or not they paid me.

I told them I was disputing this amount and I’m already getting calls from the collection agency to collect. My worry is that this will ultimately affect my credit score if I don’t resolve this, so it’s almost like I’m forced to pay them one way or another.

Any suggestions or recommendations on what I should do? For one, I think it’s BS that they claim they paid me for this sale when they don’t pay commissions for incomplete sales. Secondly, if they did pay me, this was their clerical error so why am I being held responsible for it? The company has a 180 day (6 months) chargeback period where any sale that cancels before 6 months will be deducted from your current payroll.

Appreciate any and all feedback and suggestions!