The author's life would be a lot easier by switching to a better VPS provider.
Neither DO nor Vultr actually routes the assigned prefix to your VPS, so you have to run something like ndppd [1] to answer NDP queries for IPs in the IPv6 prefix you've been assigned if you want the local router to send your VPS any traffic on those addresses.
I use Linode for work, and a local provider (binary lane) with a /56 for personal at $10 a month or less each.
If you're looking for something even smaller and cheaper than $5/mo, I've had luck with BuyVM. They've very cheap, have good customer support, a nice panel, and you get an entire /64.