ATC doesn't see my descent

[asquel 2]

This is the third time I experience the same problem : I fly IFR, and everything is OK until ATC asks me to start my descent. I do it, but he asks me then threee times to accelerate my descent, even when I am a couple of thousand feet below my previous altitude. Eventually, ATC cancels my IFR flight plan. Any one experienced that problem ?I am flying now in the area of North Quebec and Greenland, where the atmospheric pressure is very low (984 mb): would that be the cause of the problem ?Thanks for your answers.Alain