Lufthansa — Seat selection

I am trying to select or upgrade seats on an Athens to Houston flight this coming November. The Lufthansa website shows my booking, but will not let me select seats. I called the 800 customer service number and was advised that I could not select seats until 23 hours before the flight leaves. I have never had this issue in the past and find this hard to believe.

I tried the Lufthansa chat feature and it kept referring me back to the phone number that I'd already called.

I called the Lufthansa[protected] number. The automated voice stated that I could not talk to a human and that they would try to get back to me within 30 days.

It is like no one at Lufthansa cares or wants to help. How can I speak to someone with the knowledge and authority to help me? Thank you.