Unlocking GSM Phones from O2, EE, Vodafone Networks in the UK - Experiences & Processes

Hello. I would like to know if anyone knows what procedures need to be performed for English networks to unlock their phones from the o2, EE and Vodafone networks. In the UK you can find a lot of unlocking offers, all you need is to provide them only with IMEI phone numbers. Such a "service technician" reports a request to the given network for an unlocking code or for unlocking the telephone (eg Iphone). I tried one of these methods to unlock o2 phones. In two cases I succeeded, but in the next ones I got refused. If someone is able to explain all the processes involved, I would ask for contact in a private message.

Thank you and best regards.

UK networks can add phones to so-called BlackList (stolen / extorted) then it is impossible to unlock simlock cheaply.

This is clear, it's more about unblocking from the network, i.e. Unlock.

As you probably noticed, when unlocking iPhones there is a division into clear and barred. Before placing an order for unlocking, you should check whether the phone is clean or blacklisted - if it is the cost of unlocking it increases most often or there is no way to unlock the phone.

I know this difference and it is only about "clean", I know how to check and where.