There are 2 ways to watch HBO: via the cable-TV system or the Internet.
HBO via cable-TV is limited because HBO rotates movies month-to-month and apparently relies on unmotivated Content Editors to inventory its content.
Via the Internet, I've used HBO Go (pre-Max) and it appears their entire library is available to stream.
You're experiencing 1 of the limitations of HBO via cable-TV and the workaround is viewing via the Internet with Max.
First, it's not a perfect workaround because HBO Max is limited to certain platforms and if you don't have 1 of the compatible platform, you'll either need to buy 1 or wait for HBO to fix the missing episodes. Second, streaming Chernobyl via the Internet will count against your data cap. Third, it's just horrible customer service.
In case you haven't noticed, you're getting the rube-runaround. Have your tried directly contacting HBO? I didn't see a specific address for General Issues but perhaps you could use 1 of addresses and, hopefully, somebody could forward to the correct office.
help.hbomax.com/.../20
www.hbo.com/.../contact-us
UPDATE: It's odd how there isn't an address for general issue on their website but if you Internet search "hbo help email," you'd get general@hbo.com.