There are lots of reason why you can not upload.
Here are some of the more common reasons.
Are the torrents older than week or two? If yes it is likely that no-one is uploading data on that torrent because there is no demand. To say that another way once a torrent is available for more than about 3 days there are very few people trying to download the torrent.
Since you are not connectible . . . what are the sizes of the torrent(s)? If the torrent(s) are less than about 500 MB . . . it is very difficult for a non-connectible user to start uploading to new peers. When you are not connectible it takes an average of 1/2 the tracker update interval (most often the update interval is about 30 minutes) before you can connect to new peers and start uploading to them. With modern Internet speeds it if very possible that a torrent which is roughly 500MB and smaller will take a new peer less than 15 minutes to download which means you will rarely get the opportunity to upload any data to that peer.
The way the bitTorrent protocol is written the fastest peers are preferred . . . if you do not have a lot of upload speed it can be hard to upload data to new peers. This is especially true when there are a large number of seeders!
If you have any one of those issues it can be difficult to upload data to new peers. If you have any two of those issues it can be very difficult to upload data to new peers. If you have all three of those issues it is nearly impossible to upload data to new peers.
I have no idea which of these (if any) problems are occurring in your case.
The first step to correcting these issues is to forward your torrenting ports.
find your router and follow the instructions for forwarding your ports.
The next thing is to choose your torrents carefully . . . on most torrent sites about 70% - 80% of the downloads for a particular torrent occur within the first 36 - 72 hours of the torrent getting initially seeded on a site. If you need more upload . . . only download torrents which are roughly 12 hours old or younger.
If lack of upload speed is the problem there is very little which can be done to fix that. You can upgrade your connection with your current ISP . . . you can get a new ISP (if possible) . . . or you can get a seedbox (a remote high speed server that is used for torrenting). But if you take care of the other two items and you are patient you should be able to get along just fine . . . but of course that depends exactly how low your upload speed is.
If you have a different issue (there are many other possibilities) let us know and someone will try to help you out!