There are basically two kinds of bans.
1) The most common, is a channel ban. If this is what you have, then you can still connect to the network, but not join a specific channel. If this is the case, then you need to get ahold of an op in the channel and ask if they could explain why you're banned.
2) Is a network ban which can also be known as a gline, zline, gzline or kline.
If this is what you've got, then you need to check the network's webpage for assistance in getting these removed.
If you need more assistance, please specify which of the two bans you have, and the channel or network.
We can't guarantee that we can assist you in getting this resolved, but some of us are willing to try, however, it would be best if you tried on your own first.