Hi @Shweta Singh ,
The details you provided are a little vague but from PaaS standpoint, only ports 80 and 443 are open to the internet; see https://github.com/projectkudu/kudu/wiki/Azure-Web-App-sandbox#networking-restrictionsconsiderations. Similar rules apply to an app service environment, https://learn.microsoft.com/en-us/azure/app-service/environment/network-info#network-security-groups.
I'm assuming the Teltonika device requires a different random port. I would reevaluate the need for the listener and look for an alternative way, for instance a local app that listens and forwards that information on. Nonetheless, if TCP/IP listening is a core requirement, then you will have to go the IaaS route. Create a VM that will host your application and secure the VM with Firewall/NSGs for accepting traffic on that port.
Regards,
Ryan
Note: I've added additional tags to your question for greater visibility.