Why are so many customer service phone reps hard to understand in English?

I just made 2 phones calls and one was answered by a guy from Mexico and the second was some girl with a foreign accent who hung up on me before I even said one word! I called back and got a different girl with a very strong accent of some kind that couldn't understand the account number I gave her THREE TIMES!!!
I said 3805, she said, 3854, I said 3805, she said 3754, I said 3805 and she asked for other confirmation!!
EVERY FUCKING TIME I make a business call to some company I get a girl that can't speak English!!!

Why are so many customer service phone reps hard to understand in English?
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