What should one do who masturbated in Ramadan out of ignorance of its prohibition, and he does not know the number of days he committed this sin?

Scholars have differed regarding the ruling on someone who commits an act that breaks the fast out of ignorance. Some are of the view that their fast is invalidated and that they must make up for it, with the exception of new converts to Islam or those raised in the desert. Others have gone to the extent of saying that their fast is not invalidated, similar to one who forgets, citing as evidence that the obligation is not established except after the message has been conveyed. It is more prudent for you to make up the days you missed fasting.