From Mexico to belize and back

Hey there, hoping someone can help us out.

We flew from Belgium to Cancún, and from there we travelled to Belize, where we stayed for 6 days. The tourist tax was already included in our flight tickets when we first entered Mexico.

When we left Mexico the first time, an officer asked us to pay an exit fee. We didn’t pay it because we had already paid the tax with our flight. Now, after returning to Mexico from Belize, the officer at the border insisted we had to pay again. We tried to explain we already paid, but she wouldn’t listen.

So here’s our question: Do you really have to pay the tourist tax a second time just because you left Mexico for a few days and came back? It’s all very confusing, can anyone clarify this?

Thanks in advance!