Your code just ploughs along with out any respect for the messages and responses to the AT commands.
When dealing with AT Modems, you can't just pick arbitrary delays, you have to check for OK, and if ERROR or other messages come back you might need to retry, or wait querying status about whether a link or connection is viable before proceeding.
>> It is showing error instead.
What error, where? You don't even show an interaction log with the part to know where to even start debugging the issue.
