Your tests are showing pings close to what you’re seeing in-game. The LAT stat in the game is a combination of RTT and Ping, which means your ms will be inflated by approximately 10ms (you can find a full explanation of how this works from the developers here).
Since your tests are showing around 55ms, and you’re seeing 65ms in game, the data matches and we’ve already determined the most likely cause: Your ISP’s route to the server may have changed. This happens often, and I don’t know of any ISP that is required to inform you of this change. If you called them up and they said “everything is working fine,” that is probably correct, because it’s working the way they have set it up. Unfortunately, it means a slightly higher ping for you.
Edit: Changes can be the result of maintenance to the network, congestion issues, or new routing contracts your ISP has negotiated. Only your ISP would know the reason, but that information may not be available to customers.
Your ping may randomly decrease in the future if they make changes, but without data to compare what your connection looked like before versus what it looks like now, it’s hard to tell exactly how they changed it.
If this is a major concern for you, you’ll need to work with the ISP. But from the perspective of support offered here, there is no further issue to troubleshoot.