I gave up With the 3rd party CD player and bought the unit from the superb of eBay, so exactly like the one that came with it but CD rather than tape. I seem to have run in to the same problem as a lot of people as I have what I believe to be the correct code but am now locked out of it. 

What i found really helped was putting a no-cd deck BT enabled HU from Lidl/Aldi in mine. Its only half the depth of a regular HU, and i streamed music from my phone on the bt, and used the built in handsfree for my work phone. It worked perfectly, never had a problem with it. 

Even swapped it back out for the slightly dodgy HU when i traded it in. Best 50quid hu ive used.