'I was working' is the past continuous - we use this tense typically when we are storytelling or when we are talking about a specific time in the past, and often there is another action in the past simple that interrupts the action. E.g - Yesterday I was sleeping when the phone rang. 'I have been working' is the present perfect continuous which we typically use when we talk about an action which started in the past and continued until the present moment. E.g. You come home from work and see your husband looks tired. He has just been sleeping. 'hey darling how are you?' "I'm tired, I've been sleeping all afternoon". We also use the present perfect continuous when talking about an action which started in the past and continues into te present. For example "I've been painting the house all day and it's still not finished. I think it'll take another two hours to get the painting done." Hope this helps.

Look at the grammar for "past simple" and "present perfect". Forget about the continuous form here - the main issue is using present perfect (have been...).