Hello,
We recommend using WinSCP as your FTP client and making sure that ports 10000 and 10100–10109 are open for TCP traffic. Ports 10100–10109 are passive ports, so please make sure your client supports passive mode and that it is enabled. That is why we recommend WinSCP, which you can download from https://winscp.net/eng/download.php
As for slow download speeds, there could be many possible causes. Have you updated your configuration at all? We need more information than what you have provided so far in order to help.
If you are able to provide the game and the IP address of your server, that would help us investigate further.
Lastly, we do not provide refunds as stated in our Terms of Service. If you choose to cancel your account, the remaining balance will be credited to your account and can be used to purchase service again in the future.