My monitor is back from service! It was picked up on January 30th, and it has been returned today just after 6 days (4 work days). Note that the technical service's office was located in Portugal, just at the opposite side of the peninsula.
And best of all, the monitor is fixed: firmware updated, so I can now disable the Overscan feature and get a perfect 1:1 pixel mapping on the HDMI input. Kudos to the BenQ RMA service for this quick and effective service!