If you have Static IP assigned to the account, you need to change the APN settings of the modem.
Step 1. Log in to device website: 192.168.1.1
Step 2. Enter the following username and password:
Step 3. Select internet APN Management
Step 4. Below APN management, add a new APN profile by entering details below and press submit to create a new APN profile.
Profile Name: Static
Authentication: Auto Upon successful addition, a new Static APN Profile will be created.
Step 5. Go to Network connections
Under Profile, select Static.
Step 6. Submit and Restart