You should learn one really important fact about Indian culture, they are really polite, that is probably the reason they did not ask you to repeat yourself over and over. So you knew a girl at uni who was from india, well i think i know why she understood you, she was studying in the USA.
How can you base hiring standards on a bad call centre experience, very arrogant!.
And because you speak spanish and are learning Korean means jack, I know Japanese and polish, and that accounts for nothing when i travel cause i have a very strong australian accent. When i travel to america i have had to resort to pointing to a macdonalds menu cause they could not understand "diet coke" was the person behind the counter dumb? was it crap hiring standards....No! its a simple case of them not understanding my accent, I was not going to blame them, i pointed to what I wanted, we had a laugh and i got fatter from the bigmac. No matter how i tried to pronounce "diet coke" it was not going to happen. I had many of these experiences, I did not blame americans, I just accepted the fact that they were not used to a strong country australian accent.....and these people worked in customer service....like a 5 star hotel!!!
Then you have the issue of British english v American, some words mean completely different things, like Pants or fanny....look these two up in an British, Australian and American dictionary and you will realize the misunderstanding you can get into .
Come over to spain and you will realize how interesting things get, there will be lots of people that will struggle to understand you cause or your american accent. I have a french Canadian friend and a French mate, sure they both speak French but there are lots of misunderstandings from language/culture.
Anyway, the customer always things they are right.....