I'll assume "Government" == "US" since it's NOS.
Is there a government agency where I can file a complaint?
Not really. The government has started to get involved in large breaches, but they don't deal with small things. PCI requirements, which govern the protections merchants must apply around handling card data, are consent-based non-governmental restrictions. You can't get arrested for violating PCI because it's not a law.
You could certainly try to complain to consumer protection agencies, which counts as complaining, but it won't do much.
You could file a lawsuit. It will almost certainly cost you more than you can expect to gain, win or lose.
I believe my credit card is now compromised and I am going to cancel it and get it reissued.
When you do so, make it clear that the reason you're doing so is the unencrypted transmission of plaintext card data by the merchant. There are fines for PCI non-compliance, and the only chance of them kicking in is if there's a breach or if a significant pattern of complaints arises. (That said, for a towing company, the chances of complaints rising to a level that would trigger fines is near zero.)
If you can figure out who they are, and can figure out how to complain to them, you can complain to the merchant's credit card processor. The same caveats apply about nobody listening to onesie-twosie complaints; only patterns of widespread misbehavior are likely to trigger a response.
I don't believe this company has a clue about the risk they are placing their company in.
Well, they aren't really. The system only punishes egregious failures, not line-item non-compliance. Small merchants are effectively on the honor system, and aren't subjected to an impartial audit. It's not fair, but neither is life.
To be honest, it's likely that the most effective response you could have would be to approach the merchant, tell them that sending a PAN (card number) via unencrypted email is not allowed by their credit card processing agreement, and ask them to modify their systems to mask all but the last 4 digits. If you do so in a polite and non-aggressive manner, they might even do it. (If you approach them in a negative or rebuking manner, you should expect nothing to change except their willingness to tow you the next time you break down).