The service provider employees(MTN) do not know about it

an educated guess here but I suspect that the code required is a PUK code ( personal user key) it activates after 3 attempts to enter the PIN number ( personal identification number)
to get the PUK code you have to contact the service provider on another phone , provide proof that you own the account for the phone and they will give it to you

So you are trying to use CELL C south Africa sim card in MTN network locked (Contract) Phone.You don't need to contact the Cell C.You need to unlock from current network lock MTN.So call MTN service provider and get unlock code to unlock it.If they won't give the unlock code soon,visit the site Unlock-zone.com get unlock code at low cost and unlock it easily.

What is your phone brand,model,IMEI number and which country MTN network it is ?Because MTN network available in SUDAN,South Africa and many other countries.So you need to specify that also.Get unlock code for MTN network locked mobile phones from the site Onlinegsmunlock.com and unlock from service provider lock easily using the unlocking instructions in the site

Hello Ogiri007,

For you to get your puk code, check the back of your starter pack.{the starter pack is the pack which contain your sim card when you bought it.

Or you mtn customer care on 180 with an mtn number and they will provide the puk code for you.

Thanks in advance.

Basically what you need are IP address - ask MTN. Proxy Port setting enabled/disabled. Ask MTN. Proxy Port number. Ask MTN. APN. Ask MTN. All these are service provider specific and hence I have asked you to ask MTN. Other settings can be anything. Also you have to get GPRS activated on your mobile number. Ask MTN again. When you have all this inf, then set it up and happy surfing.

PUK code cannot be given by any manual or person . Its specific for each and every mobile number. Only the service provider can provide you with that PUK code.
So please contact your service provider(MTN) customer care. He will ask your details give him that for security check and you are all set to go he will provide you with PUK code .

WARNING: DO NOT TRY GIVING PUK CODE YOUR SIM WILL BE BLOCKED AND YOU CANNOT USE IT FURTHER . YOU WILL NEED TO REPLACE IT

The Puk number depends on the pin lock on the sim, the phone will still work with a different Sim card.

To unlock the Puk code you need to call the contact number for the service provider for your Sim. Alternatively you can unlock the PUK code at a local shop for a small fee, £10 or £20 in UK.

To unlock PUK, call the company that branded your Sim card.

As you know the puk code is on the certificate or in the documents that come with the simcard, to obtain the code call your phone service provider who owns the number / simcard.

Don't try to guess the puk code, entering it wrong too many times will disable the card.

I've explained more about the puk code here if your intrested.