Issue with Upload speed on LAN ports

Messages
83
Location
NA
ISP
Airtel Xstream,
I recently got Airtel Fiber connection with 40 Mbps plan. I was provided with black router made by Alphion. I came with issue that I am not getting upload speed of 40 Mbps whenever I connect via LAN.
Whenever I connect to router by wifi 5g band I get proper download and upload speeds.

I have connected TP link archer A6 via CAT 6 lan cable. And when I connect to TP-Link 5g band I get proper download speeds but upload speed I get is only 8-15 Mbps.
I first thought it might be issue of router. So I connected the LAN port from airtel router to laptop directly by the cable which was provided in box of airtel router. And the same issue arised. I got 8-15 mbps of upload speeds.

So my question is, Is the airtel modem/router faulty? And when I will file complaint which router should I insist them to put? Nokia or ZTE?
 
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