I know that for myself, when given a list of my 'good' qualities, I can easily disqualify them. I used to disqualify them by simply believing that the person didn't really know me. Then, I evolved (?) to writing them off because they were just what I'd call 'baseline human'.
Like, in my value system it's just baseline human to be as honest as you can, say what you mean, help a person in the moment if they need it...it's all under the heading called 'not being an asshole'.
This allows me the power to basically discount anything positive anyone could say about me, ever. I did a good job? Well, it was just doing my job. It was nice of me to do (fill-in-the-blank)? No, any non-asshole would have done that. So, I'm not yet able to really sit with any positives. But, I've gotten past consistently believing that I'm actually a monster - grotesque, disgusting, horrible. (still comes back on bad days, but it's limited to the bad days. Is not helped by hating my body so much)
The best I can offer is, I understand how incredibly hard it is. From my experience, I'd suggest that step one might be moving yourself past believing you are bad, just to believing that you are neutral, overall. I used to physically shudder, wave my hands, flinch, get nauseous, cover my face whenever someone said something positive about my qualities. Because I had such an extreme physical reaction, I could work just on that - so, hearing my therapist say that I was kind, and feeling that flinchy-crawly feeling, and instead of letting it race through my body, focusing on taking even breaths and just sitting calmly until my heart slowed down.
Can you notice if you have a physical reaction, whether you hear it from someone else or say it to yourself, and instead of countering the thought, work on the reaction? I can honestly say that just countering the thought was not strong enough for me, but changing my physical response was something I could do.
My heart sometimes still speeds up, and sometimes I still have a small flinch, but mostly, I'm in control of it. Now, how to get further than this, I do not know.