converting and calculating time

I'm sorry this has been asked before, and I have honestly been trying to
figure this out for hours by looking at examples and such but I'm lost.

We have this huge spreadsheet here at my new job with everyone's cell phone usage.

it's entered as 123,86
being 123 "minutes" and 86 seconds
instead of stopping at 60 it goes to 100
at the bottom we have the sum
which never ever matches with the phone bills

can anyone help me with this? it would be much appreciated

thanks

thanks for the input
it says the formula contains an error
Im probably doing something wrong