Study / Diploma of engineering is equivalent to undergraduate studies in Poland? [6]

I have been here in Warsaw, Poland since two and a half year in student visa. I applied to Społeczna Akademia Nauk for my undergraduate studies and got an acceptance letter for a bachelor in computer science. And enrolled college in 2916. But now there is been a mesh in my college, my faculty head is saying that they do not have authority from the Education Ministry Board of Poland to issue an undergraduate certificate in the completion of 3.5 years of my studies. Rather they are saying that they can only grant me a diploma of engineering certificate. And I have no choice than accepting this diploma of engineering certificate. I ask them will I be able to pursue further studies for postgraduate(Masters degree) with this certificate? And their answer was yes I can. But I doubt because in my country diploma certificate holder cannot directly join postgraduate degree. Please help me clarify this mesh and advice me regarding further studies with this certificate. Thank you in advance.