How come I cannot get my "oral" English to a native speaker level after 25 years of trying?

It is not clear why some people acquire native-like competence in the spoken aspects of a second language (pronunciation, word boundary identification, etc.). Age has been suggested as a determining factor and it certainly does play a role but there's enough research to show that it is not an absolute barrier. In short, there is no absolutely critical cut off point after which this cannot be acquired (perhaps with the exception in performance in word identification under conditions of extreme noise - as some other research seems to suggest - but not in real life situations).

Another possibility is gaps in input in the formative stages of acquisition - this certainly seems to be the case with the present case (judging by the comments). Of course, this would be exacerbated by a lack of integrative motivation (the need to fit in with a peer group).

A "thick" accent after a long stay in-country has also been hypothesized as being linked to a strong sense of identity and a link to a number of speakers who speak with a similar accent. This can generally be overcome (or at least mediated) by remedial instruction focusing on accent removal - this is something most English as a second language teacher have almost no training in.

You would also want to investigate possible other underlying difficulties with perception (e.g. make sure your hearing is fine - it may seem fine for normal interactions but have gaps in certain ranges) or cognition (dyslexia has been linked to poor L2 performance particularly when it comes to some aspects of phonology).

To answer the personal part of the question: It is doubtful that your parents 'screwed you up' but their approach may have contributed to your level of competence. This would be combined with other aspects of your situation - such as limited exposure to other speakers. A typical 12 year old transplant should be able to acquire L2 with at worst a slight accent and minimal perceptual difficulties. However, as I noted above, you could look into specialist remediation to overcome at least some parts of your issues. Assuming you watch films in English with subtitles often and are exposed to a significant amount of input in native-speaker English every day, I would say hearing issues are a strong candidate for at least a contributing factor. Otherwise, I would recommend seeking a qualified accent removal coach - try at least a few sessions and see how it goes.