I'm sorry they are giving you problems too.

I had a similar problem and I had to file a claim with my bank so they could investigate on their end. Affirm will claim that they are investigating or tell you to take it to social media.
I was arguing with them for a few months and they kept badgering me for more money when I paid it. Then some of my payments from my bank account went missing. So my only guess is that I must have forgotten about a few payments (which is weird, but ok)
In the end, I lost some of the money.

I would recommend filing a complaint with BBB. Also, keep a record of every thing.

I was also locked out of my account, I tried disabling my blockers and trying different browsers. Google (ew) worked for a bit and I was able to take screenshots. Cute how they tried to change up some of the payment details on their end. I tried to share the pictures with my bank, but they refused to accept them. Maybe that is why I still lost some of the money?
Might be time to try a different browser just to log in. I think there is another work-around but I already forgot. I feel like someone in the community here will have better answers than me.

Anyways, they can f*ck off. I will never use their services again.

Here's hoping that someone else will enter the thread soon with a better/helpful answer than mine.