I'm so stuck. What do I do about helping myself emotionally?

I am having a hard time with following through on the decision to let go of the awful things my stepfather and my guardian told me I was as a child (e.g. You’re awful; I wish you weren’t here; You talk too much and have nothing to say; The things you want are sinful and selfish; Why can’t you be what I want you to be?; You may be book smart, but you’re really stupid about life; Stop trying to act like you’re better than us/me, etc.).

In therapy, I say I’ll do it, I’ll let them go, then the tapes play again and it’s back to square one; it’s still 1981 and I’m still being told that I’m a selfish, no good, stuck up bitch by the person who’s supposed to take care of me. I can’t seem to make the tape stop and live in the present. I can’t get my guardian out of my head. My stepfather just set things up, but she was the more sustained presence in my life and said most of the awful things.

Rationally, logically, I know that all the cruelties inflicted mainly by these two people (and by my BM by not stopping her husband and not finding out if her sister was properly caring for me) were the lashings-out of unhappy and mentally disturbed people. For some reason, deep down, I still believe them, however, and I live according to those beliefs, though I haven’t seen or spoken to the “stepfather” (or my BM) in decades since I was removed from my BM’s care, and not to the aunt/guardian in 8 years. You can imagine how well that’s going, living as though their assessments of me are gospel: Underachieving, alone and scared.

I’m getting older and yet I haven’t done much of anything to prove to myself that I’m capable of what I imagine I could be or enjoy.

How did you stop the tapes and get on with living as you want without self-consciousness about every move, without self-imposed limits and guilt? I know I’m wasting time by playing those tapes repeatedly and by feeling guilty for cutting off contact with them, though that contact was extremely harmful. If you’ve had to let go, how did you follow through on that decision in a way that worked?