Hello @Dragan93, do you already have a lot of downloads on your phone? 
Maybe try deleting some of the old downloads before downloading new ones? 

https://support.deezer.com/hc/en-gb/articles/115003884605-Listen-To-Deezer-Offline

Thank you for answer. I tried that and still don't work 

How many downloads do you have on your phone? 
Can you delete them all and start again, while on wifi? 
Can you send us screenshots of what you see @Dragan93 ? 

I delete a lot of songs

@Yula If these are newly added tracks that are not downloading then I am having the same issue, there seems to be something wrong with the way Deezer handles the downloading of newly added tracks to playlists you already have download because some of the time it works other times it doesn’t, this also happens when you download your favourite tracks. I would expect that as soon as I add a new song to a playlist I have downloaded I would see the syncing notification show up and it would be downloaded immediately but this is not the case and it can be confusing. I’d also like to note that this happens with playlist made by other people that you add to your library then download, they also do not seem to auto download when they are updated with new tracks.

i have the same problem, please help me

Hello @GardenLegs when you add new song, just go on the playlist under the download music section, 

slide down the playlist to make sure it downloads the newly added song, this needs to be done while connected to your network!

Thanks for the response @Yula But the only way I can get downloads to work is if I force close Deezer then clear the cache, then open deezer back up and go to the playlist, then when I pull down to refresh it will download. I have replicated this on another phone as well so there is an issue here.