When my contractor finished the work and left, I noticed he reused the old flashing. When I call to report this, no one will return my messages. Isn’t flashing included in shingle installation?

Yes and no. Flashing is only included in installation if the contract includes it in the scope of work to be completed. If you signed a contract that did not specify new flashing, the contractor is within their rights to reuse the old flashing. This is why it’s so important to read and understand anything before you sign it.