What is the ruling on the center requesting an increase in the amount after an agreement has been reached, and am I obligated to pay it given my dissatisfaction with the service?

Firstly: Among the conditions for a valid sale is knowledge of the price; otherwise, the sale is void. Secondly: If the center that provided the service is in a country with an official currency, and the agreement was for "a thousand" without specifying its type, then "the thousand" is understood to refer to the currency commonly used in the center's country. If there are two currencies in the country, it refers to the predominant currency in that country. There is no dispute that the unqualified mention of dirhams and dinars in contracts refers to the predominant and known currency between the contracting parties.