Well that’s no reason to be unimpressed. Every phone company sells some defective devices, since no one can test all phones before shipping. You’ll get a new screen/phone for free.
This is a known issue caused by the proximity sensor being sensitive to dirt on or under the screen. Usually cleaning the screen (also from the inside) solves the issue - at least for a while. An update that may improve the sensibility of the sensor is being tested at the moment.
Post your request number here to get a fast reply.