How to connect Wi-Fi from Huawei E 3531 data card?

What I guess from your set of situation is that it may be because of the wifi router that you are using. Sometimes the router installed does not give the desired output and you are likely to have connection problems through it.
Another thing which it could be is your OS that you are using. If you are not using Windows OS, it might not work, that is what they are saying in their company website.
So, in that case you can check both these options and take the help of the customer support, from the service provider of your wifi connection.
See if that works.

As far I know Huawei E3531 data card doesn't comes with inbuilt WiFi. You will need to get a router for creating a WiFi hotspot. Here are the steps to start a WiFi hotspot.

1. Get a WiFi Router which supports hotspot functionality and install its driver.
2. Go to command prompt type "netsh wlan set hostednetwork mode=allow ssid={You WiFi name} key={You password}"
3. After that type "netsh wlan start hostednetwork"
4. Then your hosted network will start but till now it is not configured to share internet connection. To do this you have to go to Network Connection -> Adapter setting.
5. Find you current internet connection or dialup, after opening it click on sharing and share it with your WiFi hotspot.
6. Now restart your PC and repeat 3 Step.
7. Now you are good to go.

Note: - To stop WiFi hotspot use following command "netsh wlan stop hostednetwork"