So, you have all accepted this and no one said anything;
they are lying, like in day, they say its night and no one says anything;
They should say the truth that there is no UNLIMITED PLAN at the first time, not at the end
The word unlimited with almost all ISPs in India - and indeed many ISPs in many countries outside of India - is nothing more than a marketing ploy. In India, Airtel are fairly notorious for having started this trend and being one of the most obvious about what they are doing.
While the plan is still unlimited, they really mean "use as much as you like, but don't saturate the line 24/7" - if you had an unlimited electricity connection, would you leave all of your lights and appliances on 24 hours a day? Maybe not. Or if you had unlimited phone, would you be on the phone 24 hours a day? I doubt that you would do that either.
In some ways, an FUP is good - bandwidth is much more expensive in India than a large number of countries (mostly in Europe and North America of course), so reducing the speed after your "fair use" allows ISPs to mitigate the economic effects of people who do want to utilize the line 24/7.
In other ways, an FUP is bad because in India they are usually quite restrictive and poorly implemented and are usually nowhere even close to the cost parity as I know the costs of wholesale bandwidth and building a network to be.
In fact in some cases the large ISPs are making close to 300% when we count the amount of GBs on offer... but they have other costs which I don't take in to account as much for my company (large amounts of
TV airtime, large workforce, building $100 million tech-parks all over the place to house said workforce), but then some of their direct costs would be cheaper... you know, owning the international infrastructure and all, their per-GB price is bound to be better than mine
The overall problem is more of a marketing one than anything else: use of the word "unlimited" implies unlimited usage. In my country (New Zealand), they couldn't say that, they had to use "flat-rate", which refers only to the price - the ISP usually states fairly prominently that they have the right to implement traffic shaping during certain times of the day and so forth, which they do, very heavily.
We take the same approach as the Kiwis in our marketing (as I am one) but as of now the GB limit at which we might consider throttling the speed of a customer is merely hypothetical
In other words, I agree for the most part with what you say:
They should say the truth that there is no UNLIMITED PLAN at the first time, not at the end