World can't be download in Minecraft Edition Pocket

Hello  My daughter just bought new worlds and other items from the shop. The money (coins) have gone but the items can't be downloaded. When we try to start a new world we can see those items as "download" but when we click on it the download bar doesn't progress at all. Is there any tricks we can try to make those downloads successful? Afterwards she tried to uninstall Minecraft and install it again but worlds have gone completely and off course coins/money is not back   Thanks a lot for your help. Olivier PS: sorry for the wording as our game is in French and I am not sure my message is clear