Vodafone — Vodafone postpaid bill after port out

I had ported out of Vodafone postpaid on 13th August by paying all dues and having no outstanding amounts against my account.
2 weeks later the vodafone officials called and asked me to pay an hefty amount which was double the monthly amount that I used to pay while using vodafone postpaid. In the bill, I came across various undisclosed heads that had caused such an hefty bill amount. Such heads were classified as "Value added services" which the officials refused to further explain upon.
To avoid any inconvenience and harassment in future from Vodafone, which was a very frequent thing in my tenure with Vodafone...I decided to act as per their terms and paid the hefty some on that very day they had asked me to pay.
Even after such payment, even today I am receiving calls and text messages even whatsapp from Vodafone to pay such an amount again. Why should I face such an harassment in my busy schedule?! Such inconvenience and injustice being caused to me by such a horrible telecom company. In need of assistance.