When I was doing internship at Customer help desk in the bank I usually received complaints. You need to re-phrase this first sentence as it sounds as if people were complaining about YOU! 'During an internship at the bank's Customer Help Desk, I usually dealt with customer complaints.'
You need to remember to use 'the' and 'a' when necessary: the electronic transfer...the Information System office...After a probe (an investigation would be a better word)...
A few other areas need a check as well...
He had telephoned the bank...but to no avail. In his anger....cut the words 'where I was present'....I would help him and apologised for any inconvenience...showed him how to electronicaly...I phoned him and said that if he ever has another problem...