Step-by-step explanation:
I am not quite sure what the question here is, but the stated claim is false, so I'm assuming it has something to do with its revision.
The word "as" here suggests that two actions happend at the same time (calling mum and turning the car around). This, on the other hand means that both these actions need to be expressed in the same tense.
Since the verb "turned" is in the past tense, that suggests that the verb "call" should also be, meaning that the correct answer is "called".
So, the claim is false, because the verb should be in the past tense because the action also takes place in the past