Yes, you should upgrade to V-Fiber and you will get the 100gb every month. Regarding the modem you should demand for a free one since you are an old loyal customer. There are members in this forum who got the modem for free without paying anything.
Regarding Chromecast it should work, but I am not sure myself, maybe someone else can clarify that for you.
Thanks for your reply. The option they gave me was 1000GB valid for a year the 100GB per month I got to know through this thread. I don't know if they are willing to give me that. I will have to mail them and ask for it. But which option do you feel is better the lump sum 1000GB or 100GB extra per month? Regarding the modem how does one go about asking for free? Does one ask for a rs 100 discount per month for 5months? The customer care people who call with these offers generally just say "sorry sir, such offer not available". My other hesitation for not paying rs 500 is that hathway is now offering no FUP 25-30MBPS connection per month for rs 999 which costs less than my current plan with FUP. I can use the money to buy a new connection instead. But hathway is unchartered territory for me. Any suggestions? Getting really confused.