SHL: That’s right — many native speakers have never heard of it. The IPA is /ə/. You’ll find that symbol in any good English dictionary. It is the neutral vowel that almost any non-stressed vowel can be reduced to in English. For example, “lesson” and “lessen” sound exactly the same in all standard varieties of English. So do “then” and “than” (when unstressed).

German also has a schwa (in fact, the word, originally from Hebrew, first entered European languages via German, hence the spelling), so it’s not an issue for Germans, but Spanish most definitely does not have one, and it can be a major issue. (Actually, the schwa in German tends to be between /ə/ and /ɛ/, which may explain why it’s almost always spelled “e” in standard German. Also, the German unstressed “er” can be considered a type of schwa — IPA/ɐ/ to be precise — although Germans are very careful to distinguish the two.)

Here are three pieces of pronunciation advice for all ESL learners:

1. Master the schwa — the most common sound in the English language (that even many native speakers have never heard of).

2. Master the schwa.

3. Master the schwa.

That being said, if you’ll upload a video at https://vocaroo.com, I’ll be happy to tell you exactly what you need to work on. There are consonants, vowels, word stress (English has three levels), rhythm, intonation, phrase / sentence stress, and so on. There’s a young lady from Chile who posts audios regularly, and she’s been making steady progress. If time is of the essence, you may want to consider a lesson with a teacher knowledgeable about English phonology.

By the way, in real life, people often confuse accent and pronunciation, so we don’t really know what the interviewer was truly referring to — he may even have chosen the wrong word deliberately. To me “articulation” has more to do with pronunciation than with accent. Accurate pronunciation is essential to both speaking and listening, and it’s best to take care of it ASAP, unless you plan on unlearning and relearning everything you know at some time in the future.

Corrections to your text: The sentence “I wasn’t hired because of my accent” is grammatically correct and completely natural. It is, however, incredibly ambiguous. From the context, it’s clear you mean that because of your accent, you weren’t hired, but another interpretation would theoretically be that you were hired, but your accent was not the reason.

"It is a ridiculous demand which England and America make, that you shall speak so that they can understand you".  --  Henry David Thoreau, Walden, 1846

I like accents, but contrary to the opinion of Jeanne, it has been my experience that many Americans do not, especially when they are seeking help desk support.  Some are just impatient, some resent that the corporations have outsourced so many "American" jobs to foreign countries to save money, and some are just ignorant racists that don't like anybody who isn't like them.  I think it's inevitable that you will encounter some of these if you work in the call center business.  We are living, after all, in a world where our president tells us that everyone in El Salvador is MS-13 and that they would all move here tomorrow if we let them.  I would like to think that the vast majority of Americans think that this is ridiculous but the results of the last election suggest otherwise.

Many businesses in the US advertise that they have US-based call support to attract those customers that don't want to deal with even the slightest of language barriers.  I have a friend who manages a call center that fields calls from a wide variety of corporate clients.  He has a hard time finding enough employees to staff his call center because a lot of native English speakers don't speak English well enough to satisfy his clients.  They sometimes complain that his operators sound too "urban".  He often jokes that he has to train people to speak "Suburban American".

I think that it will be hard to learn "Suburban American" and not worth the effort.  My advice is that you should concentrate on improving your vocabulary and becoming fluent, and not worry about your accent.  Call centers are going to need bilingual people who can speak Spanish without an accent.