Do you know if it had a static IP on the WAN port? If so and you changed ISP's you will need to either reset it to use DHCP or a new static if this new provider is providing one.   You can set the WAN IP using the local status page of the MX https://documentation.meraki.com/General_Administration/Tools_and_Troubleshooting/Using_the_Cisco_Meraki_Device_Local_Status_Page#MX_Series_with_Single_Dedicated_WAN_Link ... View more