Hello,
Which server are you attempting to connect to?
Please let me know, thanks!

s210 I'm in China. I tried using VPN but the problem still exists

it seems to have good connectivity periods once in a while, but it doesn't last long

OK, your server seems to be stable from my end with no hiccups or interruptions in service. Unfortunately, this means you most likely have a bad connection to the game servers (not the same as a bad internet connection).

Please try these steps to see if the issue can be resolved (please make sure to do all steps and do not skip any):

1) Clear the Client Cache

You can clear the cache of the mini-client by clicking the cog icon in the top right of the game screen and then choosing 'clean up system'

2) Flush your DNS Cache

To flush the DNS cache, you will need to click on the 'Start' *on, then 'Run' and type 'cmd' and hit enter.

When the Command Prompt screen appears, type 'ipconfig /flushdns' and hit enter.

3) Reboot the PC (To be extra sure, reboot the Modem/Router too)

If doing that doesn't fix it, you may need to try VPN programs (and all of the servers the programs have available to you) or contacting your ISP for assistance. I know you said you tried a VPN, but you need to try a large number and broad variety of them to find one that routes you around whatever problem you are experiencing.

In extreme cases, if a VPN does not work it often means that the outage is too close to you to be routed around, meaning you will have to wait until it is fixed. :( I would again recommend contacting your ISP in this scenario.