"bill me later" division of paypal paypal, WebBank approved a purchase, then disapproved after I was obligated to buy salt lake city, Utah

This is in regard to a transaction on ebay in December, 2012.  "bill me later" gave instant approval for a rather large purchase to be on their 18 month no interest plan that was in effect at that time.  

After this approval, I was obligated to purchase the item.  When I tried to complete the purchase, suddenly it was not allowed.  I tried again a few times, again getting instant approval, and then denied.  The message i received was to use a different payment method, so I had to use my other Paypal account (credit card).  

I contacted the company, and when I finally spoke to a live person, I had to give them all kinds of personal information.  They then informed me that they thought someone was trying to commit fraud, but now that they knew I was who I said I was, I could now use it.  I told them I had paid for the purchase on my other Paypal account, and could the one account be credited so I could use the "bill me later" plan.  I was told that I could feel free to use "bill me later" in the future, and the call was terminated.  

I sent two further requests in writing for them to correct the situation with no response.  Now I am stuck with a large credit card bill with high interest charges.  I would advise against using this Paypal unit based upon my negative experience.