So, you are keen to know with regard to seniority and promotion!!!
First of all, the seniority has to be reckoned with reference to the date of appointment in a particular cadre. Here, you were appointed in the cadre of "Clerk", whereas, the post that was advertised and filled up is a post higher than the clerk. The employer has a right to fill in the post either by promotion, or by direct recruitment. But, promotion from lower post to higher post depends upon the rules relating to conditions of services and or promotion. Admittedly, as said by you, there is no channel of promotion in the society. Hence, you cannot claim promotion. (However, the matter of promotion depends upon the rules framed)
You could have applied in response to the advertisement and preferred to appear before the authority, provided you were possessing the required qualifications and experience. It appears, you have missed the Bus. There is hardly any substance in the case, and accordingly, I do not think that you have a sound case on merits. Even if you agitate, the claim in all probabilities will be dismissed as "totally meritless".