I got a VPS from Stromonic in Dec 2021 and paid for a year upfront. Provisioning was fast (about 4 hours) and flawless. Even IPv6 was enabled by default. It performed decently: Xeon CPU, storage was fast, nothing to complain about. Their network had some short hiccups from time to time but that's common between India/Asia and Europe, I guess.
In March there was a longer outage in March '22, but their support team was able to resolve it within 2 hours after opening a ticket.

On Sep 13 I filed a cancellation request in Stromonic's WHMCS portal and they confirmed they would cancel the server on Dec 9 which is the end of the period I paid for.
On Sep 23 I discovered that my VPS with them was offline. I decided to postpone looking into that since I was on vacation at that time.

On Sep 30 I logged in to their customer portal and found my VPS terminated. I opened a ticket and they just responded that they've terminated it due to my cancellation request. When I pointed their attention to the cancellation date they confirmed via email, they created a new service for me. My server and all data on it was already deleted.

We went back and forth a bit but they refused to give me any reason why they've cancelled my server early and also didn't seem to see any issue in their practice. So I've decided not to use the new server they've set up and asked for a refund instead which they've refused.

So that's my experience with Stromonic with an unhappy end. You may decide on your own whether you'd like to deal with a company not honoring the periods you've paid for.