As many have pointed out, closing Millennia isn't a good idea. It's only GST every year if you can't spent 1 lac.
I'll suggest 2 things:
1. Call CC and request to raise an LTF request for you. They will say it won't be processed then simply tell them "that's fine, please just open an LTF request for me, thank you". Be very polite. Once they raise the request, it'll be successful most probably. I've converted my Millennia and UPI cards LTF just like this 2 months ago.
2. Once the request is closed, convert the card to Rupay. It'll help you reach the milestones faster.
Also, you'll get reward points if you've paid the annual fee.
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