Boot into your BIOS and look to see what it says in there. If both your BIOS and CPU-Z report that speed, then they are both correct.
You may need to update your BIOS to use that particular type/kind of memory.
Check with motherboard's support website to see if the RAM you have is "QVL" (that means certified to work in your motherboard, by your motherboard's manufacturer)
DOesn't sound like your DRAM is set correctly - if you have an Intel rig go into the BIOS in the advanced area and enable XMP and select Profile 1 - if it's an AMD Rig, look for DOCP, EOCP or XMP and use it to set the DRAM to 1600