score:4
They refused this application under Paragraph V 4.2 (a) and Paragraph V 4.2 (e) of the rules. The show stopper was V 4.2 (e) which currently says...
must have sufficient funds to cover all reasonable costs in relation to their visit without working or accessing public funds. This includes the cost of the return or onward journey, any costs relating to dependants, and the cost of planned activities such as private medical treatment.
Based upon the evidence you listed in your question, we can start eliminating...
So that leaves your invitation letter as the only evidence they were obliged to consider. It's a weak position to be in. You didn't give the name of the company (and we don't want it by the way), but it's likely they would check to see how well they know that company and if they had a good sponsorship history and if they had the capacity to offer you a job. "Capacity" in the legal sense of the word, i.e., they had a license to bring in visa nationals for a work permit and they had enough experience doing it to be trustworthy. Whatever they found was not enough to carry the application and the application became imperiled at that point.
They went on to look at your "personal circumstances". This means things like your job and apparent life-style. You have no employment history, probably not married, probably male, living with your parents, not leading an independent life, and all the rest. "Personal circumstances" also can include your immigration status in Greece, but with all the rest and based upon what you wrote, you hit almost every trigger as a high risk applicant. In the vernacular, it was a 'no brainer'.
Finally, you applied back-to-back without changing your 'personal circumstances' when the first refusal raised credibility issues. That drew a second refusal and now matters are worse.
Some random points...