Is a training failure a disciplinary offense?

I worked for an oil and gas company. When I signed my permanent contract, nothing on it stated that I would have my contract terminated if I happened to fail some in house training. I failed once and I was given a second. But before that, I was threatened with a warning letter, stipulating that in case of a second failure a disciplinary process would be against me. I did not sign it. During my training, I believed I was discriminated and made a complain to the company HR headquarters. They promptly told me an investigation would be done within two weeks. But it took way longer and when I decided to inquire about the progress of the investigation, I was told there were still no results. The next morning, my local HR department informs me verbally that the investigation was concluded and there was no discrimination. No investigation report or proof, that an investigation was carried out, shown to me. But they decided to open a disciplinary process against me. 1. My contract never stipulated that it could be terminated if I happened to fail at school. 2. An investigation was supposedly done to investigation the circumstances behind my second failure. I was verbally told it was concluded and there was no discrimination. No report is shown to me. 3. I did not sign any warning letter. 4. Is a training failure a disciplinary offence?