Linguistic borrowing is a funny thing.
Old English borrowed "cell" from Latin CELLA, in the sense of a small room (e.g. a monk's cell). Modern English, too, has the word "cell" in the same sense; the more frequent sense "smallest unit of an organism" is derived from it. But Modern English "cell" cannot be the descendant of Old English "cell".
Old English "c" originally always represented the sound [k], but underwent palatalization before the front vowels "i" and "e" to [tʃ], the sound written "ch" in Modern English. This happened within the Old English period itself, though not reflected in the spelling until much later. For example, the analogous Old English borrowing "cist" < Latin CISTA appears in Modern English as "chest". So if "cell" had survived into Modern English, it would be spelled "chell" and pronounced accordingly: [tʃɛl].
In French, of course, original Latin [k] was similarly palatalized, but to [s], which accounts for most of the words written with "c" and pronounced [s] in English today. Since English "cell" is indeed pronounced [sɛl], it must be a French borrowing that replaced the inherited form [tʃɛl].
"Every word has its own story."