Have you run the setup / configuration routine for your router? Download the manual -
DIR-868L Wireless AC1750 Dual-Band Gigabit Cloud Router with AC SmartBeamTM Technology | D-Link UK and read the configuration section.
Do you know if you use a static or a DHCP assigned address on the laptop? Open a command prompt on the laptop and run ipconfig /all and look for DHCP, it will be either yes or no.
You may need to clone the laptop MAC address for the router to talk to the cable modem.
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