I have a question regarding this circuit;

Now the values of U = 10V and R1 = 150 Ohm R2 = 470 Ohm and R3 = 330 Ohm.

Consider the case that S1 closes the circuit and the current flows through the resistor R3 as well. I was calculating the voltage at R3 and I did so successfully using the Kirchoffs Loop Law.The voltage should be U3 = 5,65V. But here is the Problem that was bothering me.

I first tried doing it like this. I new that R1 and R2 were in series so I calculated that the current has to be I = U/R1+R2; since R3 and R2 are parallel they should have the same voltage;hence calculating U2 would give me U3.So I tried U2 = I * R2 and I got the wrong result.Than I kept trying and trying and I solved it so that I calculated U1 = I * R1 and than I used 2 Loops to get the value of U2 and it turns out U2 was equal to U3.

Now my question is why didnt my first method work? If I was able to calculate U1 = R1 * I why didnt it work for U2 = R2 * I when the same current is flowing through both of them?

I know that the answer is probably trivial to most of you but that I am just starting out this is very unlogical to me and an explanation would help.

Thanks!