You disputed a valid item. Not good.
This may have been what happened.
The score is usually about 45 to 60 days behind on your activity.
You may have disputed the amount, seen an increase in your score from your dispute (for 30 days), then the item comes back as verified and damages your score.
Also credit bureaus make notations that you do not see about your disputes.
I read, that you get a "grade". So if you have real issues someday, you will not get the respect you deserve.
Never dispute valid items again. It makes no sense
That seminar stole your money...
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Could you give the name of the company?
Im curious if they have any complaints on the internet