\(f\left(-1\right)=-4\Rightarrow-1+a-b+c=-4\)
\(\Rightarrow a-b+c=-3\)
\(f\left(2\right)=5\Rightarrow8+4a+2b+c=5\Rightarrow4a+2b+c=-3\)
\(\Rightarrow3a+3b=0\Rightarrow a=-b\)
\(\Rightarrow a^{2019}=-b^{2019}\Rightarrow a^{2019}+b^{2019}=0\)
\(\Rightarrow A=0\)