This service is currently not available on the Telecel network as their system is set to show your number when you make a call. Either they had to pay a little extra for this feature, or it is a fault of their system - I strongly believe the former as contract lines (and Telecel employee's numbers can hide their numbers).
If you try and "hide" your number on a Telecel sim, your calls will not go through and tell you to contact the operator.
Your best option is to make use of someone else's phone to make the call