If you paid the fine and got points already, this notice of hearing can't be to simply pay the ticket (you already did that). Look on the paper, find the docket number and look up what the case is about. You may also want to call the local court. If you cannot solve the problem that way, call a local attorney who can advise you about how to handle the situation, he will most likely be able to appear on your behalf.
A Wisconsin attorney would be able to address this best. It sounds very odd that they would make you appear if you've already paid the fine and plead guilty to the offense, but every state has its quirks. Hopefully, local counsel will be able to appear on your behalf or can arrange for you to appear via phone, but that all depends on the judge. Most that I encounter here in central PA require personal attendance if a hearing has been scheduled.
If this was written as a criminal speeding violation it will not be as simple as just paying a fine and calling it a day. If this is the case, you will likely be required to appear or need to have an attorney appear on your behalf. If it was just civil, you will probably be able to resolve most of this over the phone, but an attorney in your state will better be able to assist you in the process.
The best thing you can do is contact a local (Wisconsin) defense attorney. Many attorneys are willing to discuss your case and explain why you do or do not need to appear for court.