I was connected to 100mbps local city cable internet. but speed i am getting in

You are connected to 100mbps because when you plug in the cable, it detected 100mbps? It's actually not. It's just the speed and duplex it can connect with. Also, you need to see if there's anything wrong with the network settings and router. There's so many details you need to look into. Please provide us more information so we could help you out. Thank you.