Taxpayers harassed twice

Income Tax & Value Added Tax (VAT) of a business is assessed on the basis of sale or turnover. This is unbelievable but believe it that in Bangladesh the sale or turnover of a business is always assessed twice by two different govt. departments & the sale or turnover figure assessed by the two departments for the same business is always different! This funny thing is happening because Income Tax & VAT are assessed by income tax & customs department respectively and there is no co-ordination between the two departments. As a result, a businessman is harassed twice for the same business, which is completely unnecessary.
The customs department should handle the duty & tax of goods being exported or imported, to or from other countries only, not inland tax (VAT or sales tax). As far as I know, Bangladesh is the only country in the world where inland tax (VAT or Sales Tax) is collected by the customs department. Around the world, inland tax (VAT or sales tax) is collected by the income tax department along with their regular income tax collection, and thus a businessman is not harassed twice.