At what point will the tribunal service contact me

Hi I sent my pip mandatory reconsideration and sscs1 to the tribunal service just over three weeks ago, and it was signed for the next day, since then I've not heard anything, should I have heard off them by now to say that the appeal has been accepted and what happens next, or am I being impatient and it takes a little longer, many thanks for your help.

Thank you Gary for your advice, I rung the tribunals service today and the lady I spoke to told me there is a backlog, so to ring back when I get to the month point of sending it which will be next week.