For a convenience sample, the population in the sample is available at the moment the research takes place. An example of this type of sampling is when someone stands at the exit of a store and polls the customers leaving the store.
So, we see that's not the case for this problem.
Otherwise, for a voluntary sample, the researcher chooses members from a group to participate in a survey. But those members can decline to answer if they are not available. In the previous example, they could also decline, but would at least have to say "sorry, I don't want to participate".
In the case of a voluntary sample, the researcher can try to call people or give provide them a website, for instance, where they could give their opinion if they choose to.
As we can see, this is exactly the case of this problem. In this case, the customer can choose not to answer the call, or maybe they won't even listen that someone is trying to call them.
This type of survey is not random, because the population that participates tends to be formed by people who don't work or at least have generally some free time at the time the survey happens. Therefore, it's probably biased.
So, options C and D couldn't be the case for this problem.
Thus, option A is correct.