fire4511 gave you a very practical and sensible response, but I disagree. As a tenant of an apartment or rental property, you have specific rights of possession. Even when you rent a room in a hotel, you have specific rights and entitlements to that bit of real estate (these are usually posted inside the door). You have a legally guaranteed right to occupy and enjoy. You have a right to park your car in your parking space, period. Regardless of sticker.
Go to the apartment manager and show proof of ownership of the towed vehicle. Explain the situation. Be calm and businesslike. Establish a time window that makes it impossible to have gotten a sticker. Ask the manager to call the towing company and get the car back.
If the manager refuses, threaten to send written notification to your state's Department of Real Estate. Your state's DoRE is required by law to respond to your written complaint, which triggers legal action and becomes an expense to your landlord.
The towing company is a customer of your landlord, and should be willing to return the car as a good faith practice. All you need to do is ask. If the property manager is unwilling, spring the car to save further storage, but assure the manager of repercussion. Send the letter. Go to small claims court. Take them to task.
YOU pay the landlord's mortgage. THEY should appreciate that, and work to find exceptions. If they can not do this, go to court and ask for triple damages. Most judges will find in your favor.