Don't panic! This stuff happens all the time.
All you need to do is contact your insurers (as at the time of the accident). They may need to take details of the papers you have received (the court's claim number, date of issue - the date stamped on the court papers etc) or may simply tell you to send them on by post.
Don't under any circumstances contact the court (am sure you wouldn't but you'd be surprised at the number of people who do). Your insurers will pass the papers to their solicitors to deal with (in fact it's quite likely that they have already appointed solicitors, and have just been waiting for the court docs to come through). They will deal with everything, and any damages/costs will be paid by your insurers.
As to why this has come to you, and so long after the accident, there are 2 reasons. Firstly, the Claimant's solicitors can only serve the court papers on the Defendant (ie you) or their nominated solicitors. If your insurers haven't appointed solicitors, or notified the Claimant's solicitors of those details, the only alternative is for the court to send the docs to you direct.
That doesn't mean of course that any costs or damages are payable by you. This is all covered by your insurers.
As to the timing, you have a maximum of 3 years from the date of an accident to 'settle' a claim for injury ie for the solicitors and insurers to reach an agreement on liability and/or damages. If either or both cant be agreed in the 3 years, then you have to issue court proceedings. Most claims get concluded in the 3 years, but there are a few which for one reason or another don't.
The details being wrong is a common issue, usually down to the Claimant taking the wrong details at the time. or giving the wrong info to their solicitors, or the solicitors making a clerical error. Given that you are aware of the accident, and dont dispute the circumstances, that you were there, or that it was your fault, the fact some of the details are wrong is, in the scheme of things not going to make much difference. You would be surprised at the amount of errors that do get made in court documents!
Sorry that turned into a bit of an essay....can you tell what I do for a living?