After processed, got total transparent slides ?!!

hi,

i had a roll of Kodak EB-3 developed by a local lab. but the result is
so weird, except 5 frames in the beginning, all remainds exposures
are
total transparent plastic with only ( not very ) dard strips sperated
each of them in the normal vertical border positions.

the lab said, i over exposured. i don't believe that. to make the
darkest part of the subject as total transparent, it need about 7 stops
of over-exposure, and because i use my camera always in M mode, it
sounds impossible.

but i checked my camera, and exposured another roll of cheap negative,
found no problem.

so i want to know, what possiblly the fault came from? can the
processing itself cause the result? thanks.