This sounds confusing.
Here's how to figure out what it should be....
Get you tax statment. On it, should be a "tax rate". Also, you will see special assessments such as mosquito vector, Mello Roos, 1918 bond, etc.
Make sure the "taxable amount" is your purchase price or very close.
Multiply the "taxable amount" by the tax rate. Then add the special assessments to that amount. Divde that sum by 12 to see what your monthly taxes should be.
Mello Roos can go up or down, but it normally doesn't. In your property hazard disclosure, it should state how much it can go up and when it is paid off.
This should tell you what you should be paying.