Is the father entitled to receive an end-of-service bonus for 20 years of work, given that he already received a bonus for the previous 10 years?

An employee must fulfill the contract and its conditions, and return any money mistakenly received from their employer, based on the Almighty’s sayings: (O YOU WHO HAVE BELIEVED, FULFILL [ALL] CONTRACTS) and (INDEED, ALLAH COMMANDS YOU TO RENDER TRUSTS TO WHOM THEY ARE DUE) and (O YOU WHO HAVE BELIEVED, DO NOT BETRAY ALLAH AND THE MESSENGER OR BETRAY YOUR TRUSTS WHILE YOU KNOW [THE CONSEQUENCE]) and (O YOU WHO HAVE BELIEVED, DO NOT CONSUME ONE ANOTHER'S PROPERTIES UNLAWFULLY). If your father has already received an end-of-service bonus for the past period, he is not permitted to take it again unless with the employer's approval. If the employer has withheld any of his dues, he should inquire about the reason and strive to reclaim his right, rather than taking what is unlawful for him.