Most of locked modem always provide us to enter Unlocking Code 10 attempts. If those attempts are run out because of wrong attempts, your modem would has no more chance to be unlocked any more.
If your modem was manufactured by Huawei, it's your good luck now. There is a tool which has been made by Bojs and team, for Huawei modem only, to reset the unlocking counter 0 to 10 attempts follow the guide :
1. Download Huawei Modem Unlocker by Bojs 5.7.7 which is provided at the end of the article.
2. Plug your modem to your PC and Extract and Run the Huawei Modem Unlocker.
3). Try to choose COM Port one by one and Press READ MDM DATA ( Until the reading RESULT look similar to the above picture.
4). In SERVICE, Check the RESET COUNTER and Press SERVICE.
5). Now the unlocking attempt will be resetted from 0 to 10.
Now you can unlock you modem through normal procedure which is described.
Download Huawei Modem Unlocker by Bojs 5.7.7
This method is not working for my model e1750..