Yes, there was no hack, the first site never bothered to verify what you wrote and others simply followed it. Vodafone removed these plans as there was validity error with Rs 67 and Rs 78 plan because cheaper plan was having longer validity.
I never rely on Vodafone. Hence I clearly called out in my original post that one should verify by calling them up first:
While this is officially mentioned on their website, users wishing to avail the offer may please Contact Customer Care on phone, before proceeding to recharge.
Source: Prepaid Recharge Plans | Best Prepaid Plans on Prepaid Data, Talktime | Vodafone India
Vodafone has gone from bad to worse to worst now. One of the largest telecom companies in India can't keep correct information on their website - that too on the page which provides Online Recharge?? Very difficult to digest. The screenshot in Original Post also mentions "90 days Service Validity" which further confuses the user.
Like I said, they also revised the Talktime Recharges, and Rs100 of more recharges now came with 28 days Service Validity. I tested this myself, during 17-Apr-2020 AmazonPay Flash Sale of 100% Cashback up to Rs 100, I recharged my Vodafone Number whose validity had expired, with Rs 100. I got Rs 81.75 talktime (unrestricted validity) and 28 days Service Validity as mentioned on their website. Hence, the "Service Validity" mentioned on their website was correct for Rs 100 recharge at least.
However, after the changes to their website on 19-Apr-2020, when they brought back Rs 47 and Rs 67 Caller Tune recharges, now even the Talktime Recharges of Rs 100 and more mention "NA Service Validity". Why and how did they change is again uncertain. No information either regarding this change. I dont even know what is correct.
Yes, I saw this now, and again Rs 67 plan is showing "90 days Service Validity" when you click on Know More. This is the gross incompetence of Vodafone. If they mention this, they have to give this. But alas, who will make them understand. And incorrect information on official website - makes me ponder even more, what to trust on these days w.r.t Vodafone?!Today these plans are added on Value Added services section of their website, you can find it even without entering Vodafone number.