illustration copyright

Hi, A seller I have already purchased an illustration from, the payment received about 6 months ago. I contacted them to do another job and they told me I do not own the copyright but I can pay extra for the licence to use that. From my understanding when you have done work on PPH and payment received buyer now owns this? I do not need to apply for this? there is nothing extra to click to get that protection and it is automatic? It is correct? I just want to be clear going forward. Thank you. If you can let me know.