Trying to extend order

Hi,

I bought the Mobile Router just over 2 weeks ago, but I misunderstood how the site calculated days and ordered one day less than needed and would like to extend it, I have contacted the support email a couple of times now over the last 2 weeks and am yet to get a response.
How long should it take to get a reply from the support email as the date i am going to Japan is getting closer.

Thanks in Advanced