Here I was thinking that I was innocent until proven guilty.
There are a few issues here that you're failing to understand.
Innocent until proven guilty does not mean you can sit on your hands, do nothing, and assume that since you didn't contest the tickets that they will just go away.
Obviously, you already know that is not how it works especially after you're getting arrested for another ticket that you had either failed to appear in court to defend yourself against, or failed to pay after your failed appearance. That case is over and done with though... You paid your fines and the case was closed. (By the way, paying the fine means that you plead "guilty" and the case was closed, but that does not mean that they were
wiped from your record as you stated in post #3. It means they went on your record).
Moving along to the tickets that they claim they issued to you 2 to 3 years ago (when you were pulled over (for no tag light) and later arrested for an outstanding warrant). If you can somehow prove that the officer did not serve you with those citations (at, during or after the time that you were arrested) then you might have a claim as to whether the charges were in fact valid or not. Without such proof, you will have to stand before a judge to defend yourself against those charges... But even then, having the ability to defend yourself can only happen under the assumption that your state law does not enter a conviction against you if you failed to appear on the date stated on the citation.
Get copies of the citations and see if you can somehow prove that you were never served. If that is the case, argue the tickets as were invalid and therefore the FTAs and the collection account are both unwarranted. Otherwise, check your state law to see whether the you are entitled to a court appearance once the citations are in collection.
If so, contact the court or the collection agency and schedule a court appearance.
If you are not entitled to an appearance, then you have two choices... Either pay the fines OR risk having this matter go to another court for collection where you might not only ruin your credit further, but you might also get your license suspended, possibly even a suspension of your vehicle registration as well as having court judgement entered against you for the original amount as well as interest, penalty, late fees, collection fees, attorney fees... all put together in the same package possibly along with another warrant for your arrest.
Let meback up for a minute... You were pulled over for "no tag light"... Right? Were you told that your license was suspended at the time? That could be citation #2 which you are claiming you never received. That could only mean, and assuming that you never had your license reinstated after that arrest, that the suspension is still in effect. So contact the DMV to see if your license is good or not.