A lot of people get approved for a PGD after masters even though it's not suggested (risky) and only works for specific cases, provided it's relevant and the applicant is bonafide (recent graduate). As long as the study plan showcases that you are learning something new (non-redundant subjects) and the local options are not available.
It doesn't apply in all scenarios and varies with each person i.e an MBA graduate (general specialization) would find a hard time because they have already learnt everything and its not possible to show progression in their case.
The OP was refused citing only poor academics as a reason if it was related to the level of study it would had been mentioned. Assumptions remain as assumptions.
@Khurram_1980uk got approved for PGD for May 2021 intake after completing his masters in 2005.
@prachi167 : the VO mainly had issues with your plan of studies, not financial background. Reading backwards: "The applicant's plan of studies seems to be vague and poorly documented. The applicant doesn't seem to be sufficiently well established that the proposed studies would be a reasonable expense." I read it as you're spending a lot for something which is vague and not useful.
I'd suggest rewrite the SOP and reapply. Some third parties also can do an appeal, but am not sure how that works as there is no formal process.
Wrong, "level of establishment" was included as assets shown were only 100,000$. Money spent on tuition and living for two years alone almost equal 50,000$ and above, not convincing enough. If that was the case everyone would had been approved a visa since everyone in the world have something worth 100,000$ (not a convincing tie).