My cable broadband when connected with an ethernet cable to laptop consistently provides speed between 70-80 Mbps.

In the last 3 weeks, I have been buying, refunding, replacing routers from Online shopping portals such as Amazon and Flipkart.

So far I have managed to buy 3 TP-Link routers - Archer C7, C60, C9. None of these routers have given 60-80 Mbps speed in the 5Ghz band. The max I got was 26 Mbps from Archer c9. 

The latest one with me is now Archer C9 which I may need to replace for not providing the speeds that the ISP offer through the ethernet cable. 

As per my understanding and TP-Link technical support teams diagnosis/troubleshooting, these routers are supposed to provide  60-70 Mbps for an 80 Mbps broadband connection.

Apart from TP-Link, I tried my luck with a Netgear R6220 which provided 60-70 Mbps speed however had to return due to Internet drop out problems with Netgear firmware. 

Now I am not sure what to do ahead. Any one who can throw some light and advise in this situation ?