Over pay

This is a throw away account obviously, to protect me.

Location: texas

I worked for a financial institution for 5 years hourly paid employee. I am in texas institution is based out of PA. They front PTO and sick time Jan 1 for the entire year.

Now the nitty gritty.

In March of this year, while working (I wfh) I lost consciousness due to a very life threatening pulmonary embolism and nearly died on the clock. I was taken by ambulance to the hospital and was admitted to icu over night and a regular room 1 night. I had to go on short term disability, I had no choice but to use 1 week of time during my wait week (was not given an option to not use it) prior to that i had used a week or so because I was sick like really sick the whole month of February but didn’t realize it was a PE. Needless to say I left that company end of May, in august I got a letter stating I owe them over 2k. For over payment. I want to know is this legal given the circumstances? What happens if I dont pay it back (not able to meet deadline of November 3rd)? Do I have to repay it this year?

ETA: I used up time under FMLA I also had no choice on whether to pay myself for FMLA or not. Policy is if we have time we have to use that under fmla and if we are out of time off and sick time then we dont get paid for fmla.