How many points did it drop (what was your score before, and what is it now), and when did it drop (was it a month ago, or three months ago, etc.)?
I ask because this article (https://blog.mint.com/credit/what-happens-to-your-credit-score-when-you-dispute-items-on-your-credit...) suggests the following:
"When the XB code is present on an account, a public record, or a collection, the FICO scoring system treats it differently than it would if the account was not actively in dispute. This is where the confusion comes from. The FICO score will not allow an item that is actively being disputed to harm your score. How does it accomplish this? FICO will not consider an item with the XB code present for either its Payment History or Debt related measurements. So, if you have a credit card account with late payments and you’re disputing those late payments, the FICO score will choose to not consider those late payments. And, if you have a credit card account with a large balance and you’re disputing the balance, the FICO score will not consider the balance."
So maybe it's not the dispute (as the above suggests the dispute shouldn't hurt your score), but rather something else?