Actual expenses exceeds the Agreed Cost of Materials for Building construction

Good day to all, I am a civil engineer and recently closed a contract as a contractor of a commercial building. In our contract and during the prevailing pricing of construction materials when the contract was consummated the construction of the building based on the bills of materials amounted to P 10.0 Million, however, it turned out to be more than the first estimated cost. with this, a conflict with the owner gradually developed, because they keep on implying that there was a a bad faith/fraud on my part as the contractor of deceiving a lower cost of materials for them to enter into a contract with me. Recently they seeked a legal remedy on our dispute and charged me with ESTAFA. My question is, is there a merit on their complaint for them to sue me in court with ESTAFA? Please I badly needed your legal opinion on this. Thanks a lot!