Didn't turn in or "cancel" your car permit? Forgot to cancel your tourist (FMM) permit? You're not alone and there are answers to your dilemma - maybe. I will give you some general information that may solve your problem. If it doesn't, I sell an FAQ with more solutions in my shopping cart.
There are two different problems and government agencies involved - tourist permits and Migración (Immigration) and car (truck, RV, motorcycle) permits Hacienda (taxing authority).
A tourist permit is not a visa, but most people refer to the FMM (it used to be an FMT) tourist permit as a visa, so I will call the tourist permit a visa too. But remember, an FMM (old FMT) is a tourist permit, not an immigration visa. If you neglected to turn your FMM immigration tourist permit (visa) or permit into Mexican immigration (Migración not customs or aduana) before leaving Mexico, you will have trouble getting a new immigration permit (visa) when you return to Mexico. I know. I got caught. I paid fines. So have lots of people.
Car permit regulations have changed many times in the past few years, but the procedure to cancel them is the same. If you don't cancel your car permit before it comes due, you will forfeit the bond you put down with your credit card - AND you still cannot drive a vehicle back to Mexico until you prove that you took yours out of the country.
If you don't cancel your Mexican car permit with Hacienda or Banjército, you won't be able to drive into Mexico again. Period.
Fines for failure to surrender your immigration papers (FMM) are steep -- about $1149 MXP (Pesos) for the first month and it goes up on a graduated scale from there (very roughly $600 MXP a month). Migración (Mexican immigration) has a pretty accurate computer. They caught me for not turning the FMT's in since 1996. Fortunately, Migración let me slide on all but the most recent -- a year old. The polite Mexican immigration official only wanted $2,000 -- US dollars -- from me.
Don't panic. Keep reading. I had to go back two times to find one Mexican immigration official who was willing to negotiate. For about $312, I got cleared. I know this because when I got my next Mexican FMM tourist card, the immigration official saw that the previous ones had been canceled.
The only solution for an overdue tourist permit is to pay the fine. My FAQ has no information to help you with tourist permits. Don't order it for that.
Hacienda (the Mexican treasury department) keeps even better track of your Mexican car permits. From a confidential source, I found out that their records are tied to your name, date of birth, immigration information and vehicle VIN. So basically, you are screwed if you try to bring another car in.
Occasionally, different Mexican consulates will declare an amnesty if you show up at one. IF this happens, it is usually before the Christmas season. The consulates may not do this every year, but you can haunt their websites to see if one is planned.
If you have the same vehicle and want to drive it to Mexico again, or ever drive another vehicle to Mexico, take the original vehicle back to the border and cancel your car permit.
If you cannot drive back to the Mexican border or the car was stolen or sold in the USA, I can supply you with a working email for Hacienda that has some English-speaking operators. There is a procedure to take care of a lost Mexican vehicle permit, but it takes time - about six months. I charge a minuscule amount for this service.
Before you order - be aware that you may not like the answer, but I will give you the right answer. There are a lot of wrong answers on the Internet.
If you sold the car in Mexico, don't order the report as there is no way you will get your car permit canceled. You broke the law. If you had your car stolen for the insurance, ditto.
If your car was wrecked or stolen, things are murky. I have seen Mexican-Americans fluent in Spanish (sometimes with a calcomonia or sticker on a piece of windshield from a wrecked car) argue with the officials at the border about canceling the permit. I always saw them leave without a resolution. If you have an accident, you need to get paperwork from your insurance company and a police report. That may not even be enough as it is a bureaucratic labyrinth to cancel a permit without a car. Will my FAQ help you? Maybe. It will at least give you the address to send your info to and a phone for someone to talk to. Whether they will care, I can't say, but miracles happen. All I promise is the address.