Colorado tax return / additional documentation required

Hi all.

I live in California, but have helped my elderly/hospice mom with her Colorado tax return for many years. I created a spreadsheet to calculate her return/liability; this year I filed with TaxSlayer. (My calculations and TaxSlayer matched for federal/state).

Her tax returns are straight forward: a couple 1099r, 1099int, social security. I've been doing it easily for years. TaxSlayer has no problem with this kind of simple tax return. This year she owed ~$3000 to Colorado. (We didn't do estimated tax payment for 2025, but I already sent a big check for 2026 to avoid penalty). They electronically received our payment.

So today we received a followup letter from Colorado Dept of Revenue asking for additional documentation for the 2025 return (submitted like a month ago).. They want proof of "estimated tax credits" including "copies of front/back of each check, to confirm electronic payment …… the payments you are claiming do not match the payments we have on record". Need to submit within 21 days, etc.

This seems erroneous since we didn't provide estimated tax payments (line 26 on "estimated tax payments" was $0). The only money we sent was what we owed, when we filed.

I guess my plan is to contact them (phone?) and ask what they are asking for, because it seems they are confused?? Nothing in their letter makes sense. Any thoughts on this?

Thanks. =Mxasf=