I saw the same problem on my neighbour's SmartHub - I was unable to get to the admin page on 192.168.1.254 - we tried factory reset a few times but still unable to connect to the admin page - just timed out. They were on their third replacement SmartHub so they just ordered an Asus DSL-AC68U - up and running in minutes and no more problems. I know it costs money but I really recommend getting a third party router instead of the SmartHub just for your own sanity!
@Dave7 I'm sorry about the problems with your connection and missed engineer visit.
Is there any noise on the line when making phone calls, if there's any interference on the line it can cause the Hub to lose connection and it's best to rule out a network problem before getting new equipment.
Can you run a quiet line test by dialling 17070 from your BT Landline? If using a corded phone then the test should be quiet, if you are using a cordless phone then you may hear a low hum.