Wifi router is switching off after a min.

Looks like a common issue, not sure how it switches off on its own. I'm sick of this product. Had a cheaper modem which worked perfectly and never ever had issue. This this was a better product and bought it. Wifi range is worst even with extender where other one worked perfectly without even extender.

Can see lots of forums with exact same issue. Wished I had read them b4 buying this.