Having this same issue. Applied for the card with my actual Iberia+ account number but Chase ended up creating a new one for me anyway. This is likely because the zip code on my Chase account was the full hyphenated version vs. only 5 digits on my Iberia+ account, which I've since corrected.

I've spent way too much time on the phone with both Chase supervisors and Iberia (Madrid) with no resolution. Chase originally recommended merging the Iberia+ accounts, but according to Reddit that's a very lengthy process involving the online form and a prayer. At least one guy was able to successfully merge after months, but still hasn't received his SUB.

With that in mind, I had a conference call with Chase AND Iberia and we determined that no merge was necessary, and that it was Chase's responsibility to simply change what Iberia+ account was linked to the credit card. The Chase supervisor submitted the request to their marketing department (who is apparently responsible for this stuff), and I just heard back that they forwarded it to Iberia. So now it's back in Iberia's hands... which I'm assuming will lead nowhere.

I will earn the SUB when my statement closes tomorrow. Unless something miraculous happens, it's going to post to the new Iberia+ account Chase created - for which I only have the account number. The online password reset doesn't work for it. Has anyone figured out how to access a Chase created Iberia+ account?