(Fuswilath) 41 : 14
إِذْ جَاءَتْهُمُ الرُّسُلُ مِنْ بَيْنِ أَيْدِيهِمْ وَمِنْ خَلْفِهِمْ أَلَّا تَعْبُدُوا إِلَّا اللَّهَ ۖ قَالُوا لَوْ شَاءَ رَبُّنَا لَأَنْزَلَ مَلَائِكَةً فَإِنَّا بِمَا أُرْسِلْتُمْ بِهِ كَافِرُونَ
When their Messengers came to them from their front and from behind saying: You don’t serve except Allah; they said: If our Lord had wished, he would have sent down the angels, then indeed we are denying with what you are sent with.
Not only the people of Aad and Thamood but all disbelieving people were also really not rejecting the Messengers, but they all were rejecting the Lord’s Message Adhikr with which the Messengers were deputed. That is the meaning of ‘then indeed we are denying what you are sent with’. See explanation 23: 24-25, 44; 25: 27-30; 36; 45.