I received a letter today from PayPal saying that the amount of my purchase required a credit bureau report and so they were unable to approve me for their service. But, the purchase I made was taken out of my account over a week ago. And the website I ordered from told me it was paid and I have already received my package. I don't understand why I received this letter.

Just ignore it. The letter sounds like some sort of scam to me.

Was this an email or an actual paper letter in your mailbox? There are loads of email scammers trying to get you to log into their fake Amazon, eBay, PayPal page so they can buy stuff with your account.

Sounds like a scam letter to me

read it again - read it slowly: it doesn't say that at all.