Hr Wants Repayment For A Sign-on Bonus I Never Got

Location: DC

I recently left my tech company. I was with them for <12 months, so I have to repay part of my sign-on bonus (I can keep a pro-rated amount based on how long I was employed, but the rest I have to pay back).

They gave me the repayment agreement to sign today, which states the bonus they paid and how much I now owe back.

However, I realized after checking my pay slips that I never actually received the sign-on bonus they promised me.

I admit I never confirmed that I received this payment until now (I was only with them for ~1.5 months, I left abruptly due to personal reasons), but I am quite surprised since this is a very well-known company and I have never had this issue in my career.

Of course I did not sign the repayment agreement (since there is nothing for me to repay), and instead politely asked for proof on their end confirming if they ever sent the bonus.

And to clarify - the employment offer I signed is very, very clear in its wording that I should have received X amount in my first pay slip (I have the DocuSign that was signed by both parties). They even sent me my signed offer letter (for my own records) and referenced it in the payment agreement claiming in official language that "Pursuant to Employee's Offer Letter Dated YY/YY/YYYY, Employee received a signing bonus of $X", which I did not.

I am waiting on their response - and I know answers here may be dependent on what they say next - but I am wondering if I should take any legal action, or prepare to? Am I still entitled to the sign-on (or at least, the pro-rated portion I would have kept) despite not being an employee?