Wifi range extender Issues

I have a reasonably fast fibre optic Internet connection (70MB/S download and 20MB/S upload). The router itself isn't in an ideal position, and is in one corner of the house meaning the other side of the house receives no signal from it at all. So I bought an extender and made sure that it would support the speeds of my internet. But it is just awful. You are connected for all of 15 minutes before it decides to stop working. constant drops and god awful speeds. I have tried different plug sockets all over the house and still had the same issue. What can I do? Surely the fix can't just be 'buy a new extender' because this one was a fairly expensive NETGEAR WN3000RPv3. Any help on this would be greatly appreciated