In case this info helps: I upgraded my CF to a CSR in mid-August of 2019 and my AF posted on 12/1/19 so on the 4th "first of the month" following my upgrade. What's odd is, you upgraded in September I believe and did not follow the same pattern since you were not charged the AF on 1/1/20. I believe what's been said is that the AF should be charged in 3-6 months following an upgrade so you'd think yours should be charged on 2/1 or 3/1???
So in the article it says:
Existing cardmembers will be able to renew at the current $450 fee, as long as their renewal fee hits prior to April 1, 2020
I'd hope that they would consider you an EXISTING cardmember and that your AF will post prior to the the April 1st date. Keep us posted, hopefully you get in at the $450 number and then you won't have to worry/deal with this until this time next year!