Asha 30/40 Series :: Obtain A Security Code For 5610?

I purchased a genuine Nokia 5610 XpressMusic slide phone quite a few months ago during a trip to China. The phone worked (and is still working) perfectly well. However, several weeks back I took out the phone battery and when I replaced it all of my contacts (JUST contacts) saved in the PHONE MEMORY were missing/deleted. I was only left with what remained on my SIM card. I went to Menu>settings >security >security level >memory to try fix it, then discovered that the PHONE MEMORY was now locked and its contents protected by a security code. I certainly did NOT set any security code on my phone (I only use a PIN code to access my phone - it works fine) and now, although my phone is fully functional, I can no longer save any more contacts to my phone (because the SIM card is full and the phone memory is blocked).I've used security code generators and also the typical 1234, 12345, 0000, 4444, etc - but NONE of them work.