Problems unlocking refurbished phone and now simcard

[SHANNA15]

I bought a refurbished Samsung S9+ from a phone company online.  It was advertised as being unlocked but when it arrived my sim did not work on the new phone.

I contacted O2 and arranged for a new simcard to be sent out to me and then I contacted the company who sold me the phone who told me it may not have been unlocked and that they would send me a code to unlock it.  I was sent an eight digit number to unlock the phone. This was not accepted and I am now getting the message Invalid Simcard Network Locked. Simcard inserted and it asked for my PUK code.

I then contacted O2 and have been given an 8 digit PUK code. This is also not being accepted. My sim card is working perfectly on my old phone. Can anyone tell me if the problem is with my new phone being faulty or if it is the Sim card, how can I unlock it if the PUK is not being accepted?

Hope someone can work out what is going wrong here.  Many thanks.

[MI5]

@SHANNA15 

Your phone is hardlocked and needs a MCK code to inlock it now.

@Martin-O2 @LukasB or @TheresaV can help you.

[SHANNA15]

Hi

Thanks so much. I have messaged Martin and Theresa, so hopefully one of them can help me. Appreciate you replying so quickly.

[MI5]

You're welcome.
Good luck 🤞

[TheresaV]

Thanks for the tag @MI5 

I have replied to your message @SHANNA15