What is the ruling on taking a portion of the payment by inflating invoices submitted to a telecommunications company? And what is the ruling on increasing the invoice to customers to balance expenses if they refuse to pay the full amount?

If the customs clearance fee is due from the intermediary, then it is not permissible to collect the right from the telecom company's bills, because injustice to the intermediary does not permit taking the right from another. However, if the fee is due from the telecom company, then it is permissible to take the right from their bills based on the issue of al-Zafar (taking one's right from another's property).

This also applies to customers who refuse to pay your dues; you are allowed to collect them in the aforementioned manner.

A condition for collecting the fee by these methods is that there must be an agreement on a specific fee or a prevailing custom; otherwise, you are only entitled to the customary fee (ajrat al-mithl).