Unlatching from o2

[Campervanner64]

My partner gave me her old Huawei phone a few years ago, she was with O2 and so was I.  I'm now trying Lebara but my phone won't accept the SIM without a code. I applied to O2 for a code and got this message back.

Dear Steven Thank you for your unlatching request for IMEI........ The mobile number that you provided is....... I'm
sorry, we have not been able to unlatch your device at this time. The
reason given is: We were not able to find the details in our system, the
handset is not an O2 deviceThank you, Ursula

I can't reply to this email, so what do I do now? 

[MI5]

@Campervanner64 

It must have dropped off the system.

You will need to use any O2 sim card in it to register it again then follow guide Guide: Unlocking an O2 phone to use a different SIM card 

[Campervanner64]

I'm an active user on O2 mine isn't a lapsed account. 

[Bambino]

@Campervanner64 If you're an active O2 customer just put the sim you're currently using into the Huawei, register the phone on the network and unlock it. You can then put your sim back into your own phone.

[MI5]

@Campervanner64 

It's the phone that needs registering on the system, not you.