d句子既tense用無用錯

I have been providing assitance的tense是錯的，因為雖然感覺/意識上你想講一直以來持續地都在幫忙工程師們，但這種assistance是你的職責而不是一種行為表現的情況，所以應該用present tense寫成是fact/statement。

I provide assistance to engineers...
或更直接地寫
I assist engineers...
後面的in the company和since 2003都是多餘的。前已述職你自2003在這公司...除非你由(例如)2010年才開始轉職/受任去assist engineers才會再since多一次。

你寫的重點應是你assist engineers乜東西...工程測量?計價錢?地盤會議?地盤監工?繪圖?

第三句colleagues當然是在你company的同事，in the company又是多餘的。

結論是其實你沒有講出太多內涵：
I have been working at ABC to assist engineers since 2003. I get along with my colleagues.

你可能見別人的公司refence letter會用staff of abc company...因為那信是由公司的人事部用公司代表身份寫的，從公司的角度看你才是staff of the company。從你自己寫履歷的角度用這字看起來好像你是abc公司的老闆寫自己是一個員工。

Since joining the ABC Company in 2003, I have been providing
assistance to engineers. I get along well with my colleagues.

“provide assistance to engineers” 和 ”assist engineers” 意思不同

(

"I have been a staff of ABC Company since 2003. I have been providing
assistance for engineers in the company since 2003. I get along with
colleagues in the company."

基本上六法沒有錯o 只是可以將句子寫好些o

I have been a staff of ABC Company and providing assistance for engineers since 2003. I also get along with colleagues in the company..

or

I have been providing assistance to engineers in ABC Company since 2003. I get along with colleagues well in the company.

1,You should change " I have been providing assistance for engineers in the company since 2003" into I have been providing assistance about engineers in the company since 2003.

2,you should change "I get along with colleagues in the company" into I got along with colleagues in the company