The safest way to answer a limitation question like this is to isolate the two things being tested separately: how long, and from when.
The correct answer is 2 years from the date on which the cause of action has arisen.
Another way in is to think about why the statute would deliberately choose "cause of action" over the more obvious-seeming "date of purchase" as the starting point.
Understanding the protective purpose behind the limitation clause confirms which option genuinely reflects the law.
Hence, the correct answer is 2 years from the date on which the cause of action has arisen.