If the op sold the bass, then the buyer sold the bass, then one day the op saw it for sale and bought it back, I could see it being a problem for warranty. However if the op received the guitar back from the original sale and refunded the money, there was no sale. EBMM would be hard pressed to deny the claim. OP says to EBMM "that was a fake warranty claim I never sold my bass he must have stolen the serial number from when I showed it off online hoping to get his used bass repaired." Of course that's dishonest, but it's just to illustrate how they would have a hard time disputing a warranty claim from the OP with his name on the bill of sale.
Here is the warranty, it makes no mention of of anybody else handling the bass. Only if it's been misused or altered. Hopefully the OP registered the bass with EBMM otherwise he might not get warranty service.
Warranty | Ernie Ball Music Man