Even the most popular exchange didn't anticipate the increase in users. I am thinking for example to Kraken, Bittrex, and even Coinbase. It took months to hire more staff and it's not as simple as it seems. They first need to find qualified persons and then training them to fit their needs. It's not like if you hire someone from a call center to answer to phone calls.
I agree, I know how the process works in getting new employees, and I know those exchanges you mention are a good one in terms of customer service, but what I was referring to is the other specific exchange who lack of customer service satisfactory rate, who has the same cs issues from the past years.
Call center companies arent the same anyway, there are those who hire you and can be able to proceed to work right after you completed all the requirements including interviews. I worked in one of the call center before, and the employment procedures were long. Ive trained for more than a month for the product specific training, and another 2 weeks for performance probation in the production floor.