I don't know about the Experian Scorex PLUS Score, but for sure, your other scores are not the scores that most lenders use. I'm sorry that you've gotten burned by this.

I found this about Scorex on Experian's website:

Superior risk prediction
Until now, lenders have only had two options for effective risk scoring. Use a traditional bureau risk model that falls short in predictability or invest in a more predictive, but much more costly custom model. By using a proprietary development technique that mimics custom model development, Scorex PLUS provides a superior, more cost-effective solution. In multiple market validations with traditional risk models, Scorex PLUS performed better in over 90 percent of the head-to-head comparisons. These results demonstrated Scorex PLUS provided a stronger separation of good and bad accounts and classified more bad accounts into the worst-scoring ranges.

It looks like this is Experian's attempt to come up with competition for FICO scores.

I don't know if the Scorex PLUS score has even the slightest correlation with FICO scores, but the regular PLUS score is not used by many lenders. Does Prosper.com give any guidance about why they chose Scorex? I'm sure that they get lots of baffled applicants.