Assuming an ideal op-amp, you have \$v_1=v_2\$ (as pointed out in a comment by LvW). Also note that your second equation is wrong because there is a current into or out of the output of the op-amp, so you can't just add up the impedances of \$R_2\$ and \$C_2\$.
Introducing another unknown voltage \$v_x\$ at the output of the op-amp, you can write down three equations:
where \$v_i\$ and \$v_o\$ are the input and output voltages, respectively, and \$v_1\$ is the voltage at both inputs of the op-amp. These equations can be solved for the transfer function \$H(s)\$, i.e., for the ratio \$v_o/v_i\$. With \$C=C_1=C_2\$ and \$R=R_3=R_4\$ and \$R_1=R_2\$ you get
From the numerator of \$(1)\$ you immediately get for the notch frequency
Note that as long as you choose \$R_1=R_2\$, the actual value of these resistors doesn't show up in the transfer function.