I have worked as customer support in airtel wifi.
Let me tell you something we know nothing about these ott apps.
No one would train us or explain about these things. Not even the Team leader have a clue about these things. They would just make random guess from things mentioned in outdated support portal. The callback you talking about is made by the same staff, who also have a zero clue on how to fix it.
The best and easiest course of action you can take is by threatening to close the connection permanently. Retention team which also have no clue about it, will raise a request and maybe after that the collection team will call you and waive off the charges and maybe fix it.