I did what I had been told to do

I'll try to give you a simple idea of all this sentences) Somebody told you to do something - this action was the first, so it was previously thats why here we use past perfect. (I had been told to do) If you use - "I did" in the 1st part of the sentence you confirm that you did something what you had been told to do. If you use "I was doing" you mean particular period of time during which you were doing something. those sentnces grammatically uncorrected because in the 1st part of the sentence you use past time - action you did in the past, but in the second part of the sentence you should use past perfect because that action was before.

I was doing what I had been told to do

They are all grammatically correct - it just depends on what you're trying to say. The main thing you would want to think about is keeping the tense consistent.

The 2nd ‘to’ and ‘do’ are optional. I was doing what I’d been told. I was doing what I’d been told to. I was doing what I’d been told to do. These three talk about a specific time in the past. The following three are similar. I did what I was told to do. (Focuses more on past action) I’ve done what I was told to do. (Focuses more on current result) I did what l’d been told to do. (Focuses on past, but tells that there was a time in the past when you’d been told what to do) I’ve done what I’d been told to do. (No) I’ve done what I’ve been told to do. (Focuses on the present result of the past activity.) Most common would be I did what I was told. I’ve done what I’ve been told.