Yes: there is something quite screwy going on.
Confirm: Did OpenAI actually say “we added $10 to your account”? Because if you paid, it should be there as a credit grant line item, and you don’t have two. I think you are looking at your own.
Or it could be that your payment as “invoice” went solely to paying off a virtual or imaginary partial negative balance and never reached becoming a grant. This seems mathemathically like what is going on - your expired trial is being treated like a receivable, and sucking out of your balance.
Background
The $18.00 is the free trial credit when you initially signed up for an OpenAI service and created the login. Many did this for ChatGPT, not even knowing about the OpenAI API. It expired after three months.
Any expired amount should be “zeroed-out” in the platform billing site to be like the what OpenAI has done recently: completely hide how much prepaid balance remaining of each was “taken” - no evidence that $NNN.NN was left when OpenAI marked it expired, like my $5 API trial (OpenAI lowered the amount in 2023), or the larger grant with much more unused credit expired:

You have something different: your balance on the left side says $18 - plus it also says expired. The expired amount of the free trial is still there and seems to be counting as a negative.
So there is something wrong with that old credit grant. Did you see a $0.00 Credit balance in your organization under billing before making your first payment?
The “expected” (but unwanted) behavior for over a year is that the true payment date is hidden under credit grants, and that also people have been given until the the last day of the month as the expiration date. And that any expired amount is $0.00 balance in credit grants.
I find this screenshot from Aug 2024, with the amount of an $18.00 trial not zeroed:
There could be some kind of bug and fault in understanding with new credit balance calculation code recently introduced.
If the behavior is that unused old trials “with” a balance never removed start counting further negative instead of being ignored, it could affect more than you, a retroactive “suck even more from the balance”. That is the only possible explanation here:
- a bug concerning not ignoring remaining amounts in expired, then credits instead counting their positive balance as a negative.
Evidence of code change:
- a newly added credit that expires mid-month
Such a bug could affect ANYONE with an old account, where 2022 trial credits showed the expired balanced remaining instead of it being cleared to $0.00.
Investigation needs to be done deeper and also by OpenAI - like we could ping @PaulBellow who may have an early “free trial” credit grant to report on its appearance - and say if any “remaining” amount recently was sucked off the top of a credit balance.
BTW: Even earlier, OpenAI showed how much they expired on you:
@OpenAI_Support action:
- Stuff even more credits into this account, $18+ plus more for coverage and thanks
- Escalate higher, to whoever is coding on the payments side of things.