I'm sorry to hear about your lag issues, there can be many things that can cause lag issues in game.
Firstly, I would like to assure you we have around-the-clock monitoring of our servers to watch for technical issues that may be impacting players, recently we have had no reports or issues pertaining to lag that has been a result of our servers. When outages or issues do occur, within 30 minutes the staff are usually around to let the player base know and keep updating until the server issues is resolved.
Second, while a speed test will provide you an overview of your internet health, speed tests are generally an averaged outcome of a short period of testing that will not accurately reflect micro-disconnects that can occur which will lead to game stability issues in terms of lag. As mentioned by other players, a pingplotter test can show where connection is being compromised, often it can be a intermediary between your connection and the game servers. Usually these will be resolved within a few days by the server provider.
Third, it could be a local connection issue caused by interference on your line / from a neighboring dwelling. At my last house, despite having a 250mb down line, I had interference coming in from a neighbors line that was incorrectly setup when my issues begun. This was causing micro-disconnects in my line which made certain gaming and streaming impossible (some games have bandwidth to cover micro-drops, others don't).
Lastly, and least likely, you may have a corrupted file within your game files or mod files (if in use) which may be causing stabilization issues.
Here would be my recommended course of action:
1. Remove all mods from your Client.
2. Run a check and repair on your Client (details for these steps:)
3. Reset your modem/router as per the manufacturers guidelines.
4. If issues persist please submit a Customer Support ticket, to aid in the quick resolution to your game issues and prevent unnecessary back and forth with Customer Support in the ticketing system:
Download and Run a WGCheck and attach the files to your support ticket. The detailed instructions for this process can be found: https://na.wargaming.net/support/en/products/wows/article/19498/
This will ensure that all possible causes on our end are resolved before having to contact your ISP for investigation.
I hope this helps resolve the issue,