In this case, it is best to visit the PF office which has your account and take a hard copy form to fill out. Take the copy & original of your pp size photo , aadhaar card, PAN card, cheque copy which has your name pre printed or your bank pass book with the IFSC code, name matching with the name on Aadhaar.
Submit a letter informing that you have a PF but no UAN and collect the form, fill it out & submit it. You can take the signature of previous employer or certain bank manager, etc which the PF office can guide you.
Hope this helps. Also do post your feedback after your case resolves, so that it can help others in the same situation to know the process.
From India, Mumbai
email@example.com is an option provided by EPFO, that you can know your UAN status using your epf member id.
From India, Hyderabad