Mobile not able to register on any new network after using unlock code

[rgb_alex]

Hi, I recently purchased a Huawei P20 Pro and have been trying to get it unlocked. I visited my usual unlocker in my nearest shopping centre but he said he could not do it as it was under 6 months old.
I have since received unlock codes from Mobile Unlock online but these codes have caused more problems than they have success. The phone believes that it is unlocked but after speaking to 3 support, it appears that despite being able to make Wifi calls the phone is definitely still locked to EE.

Any help is appreciated, I attempted a factory reset and cache wipe to restore phone to locked state but this has failed and I do not know of a way to re-enter the network unlock code or if it is even possible. Do you think it is worth taking to the EE store for them to have a look at it? Or is there an alternative and hopefully less costly solution?

Thanks