while I was updating Lumia 540 with 8.1 It got automatically stopped after reaching a level of 7% and while I have a decent WiFi network still no progress is there.
I face similar problem while updating Lumia 730 to Windows 10 Mobile. I think there are some bugs in Windows 8,8.1 Mobile, which doesn't display download process completely. However check your WiFi router status, if it showing that something is downloading (don't connect any other device with Wi-Fi) then don't worry let the download to complete. Also try restarting your phone. I think it will download Windows 10 Mobile completely, not need to worry.
Did you try waiting for a long time? Usually while upgrading to Windows 10, Windows devices shows that downloads are stopped halfway (at 7%, at 54% etc.). This doesn't mean they are not downloading the updates.
This is a bug with some Windows phones that they show the download is stopped, but the updates will be downloaded in the background and will be installed in time. All you have to do is, do not cancel the update and allow the device to download the update.
If you have a program to monitor your network, it'll show that you are still downloading something.
Note: I had the same problem with Lumia 540. It showed that downloading updates are stopped at 7%. After some time, it started working, and I've downloaded 10%. Again, it stopped at 54%, and then I left the device for downloading the same. After some time, the download was complete and it prompted me whether to install the updates.