No/slow internet

Yesterday morning I woke up to no hard wired Ethernet internet from my gateway. Wi-Fi worked. I tried rebooting my hard wired desktop and gateway box several times and even changed the Ethernet cable. Nothing. So I exchanged my gateway box at an Xfinity store and got 9mb/s Ethernet. I am paying for 1 gb/s internet. Wi-Fi worked OK. I rebooted computer and gateway several times again and swapped Ethernet cables bit still 9 mb/s. This morning I got no Ethernet internet again. Please help.