This whole thing is very unclear. If the problem is that the supports
were just sitting on soil and have sunk in, then I don't see why any
new joists are needed. Just placing concrete slabs for support on the
ground is not the correct solution, nor will it pass code. But then
maybe the rest of the deck won't either.

The correct starting point here is to pour concrete footers that extend
below the frost line that the supports will rest on. Then you will
have something that will last. What else is wrong with the deck or
what else is needed to correctly support it can't be determined from
the rest of the description.