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What do you mean by "call genome via BioMart"? What package are you referring to in listDatasets command?
If you have aligned bam files you can count reads based on features you are interested in (e.g. exons, genes etc) to generate the count matrix. I use featureCounts to do this before getting to DESeq2. You can use featureCounts as a standalone program or as an R-package if you prefer that.