How to stop internal conversations (not just the inner critic)

Hi everyone, I need some pratical help please.

The thread 'Silencing the inner critic' has been immensely helpful, and I've found some helpful TEDx videos too that deal with goals / self-criticism as well as the Self-Compassion website with exercises.
But what I am struggling with is not quite in these fields.

The inner critic yes, oh, a very poisonous destructive person living in my head, that is so good at driving me to really deep depths where I often have to stop myself from further physical harm more than just a few slaps in the face.

What I've now managed to work out is, that I often get to such a place by starting to have a conversation with someone, in the voice of the real person who this problem relates to, and myself - I (have) often justified this thought process with the thoughts that I need to be, or need to feel, ready for whatever situation can come up in the future.
But as I've read yesterday, this process only provides the feeling that I am in control, but in fact does not really bring anything positive, constructive to the real world outside my head, and neither does it really influence the real world - except for having successfully brought me down so far to the level of suicidal thoughts!

My question and request for help is this, please: How do I go about stopping these conversations, and keep them from appearing in a few seconds after I managed to go 'stop, stop, stop...' and then purposefully think of the basic things around me like this morning 'stop, stop, stop... wash this cup, put the cup down, ok, now turn off the light and walk to the bedroom....'.
Am I at least on the right track?

Thanks in advance.
The only thing that's worked for me is to have a a go to song that I just start singing n my head every time I start to go do that path. Lily Allen's "F you" is my current one, just needs to be something catch and sometimes I'll change the lyrics to suit telling me to stop having these conversations, but it just breaks the cycle for me which seems to work most of the time.

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