To identify where the problem is, try connecting another bluetooth device (like another phone, or a bluetooth headset). The other device will most likely connect. If it does, try contacting the manufacturer of the dongle, they will probably have a simple solution to fix it.
If it does not connect to another device, try deleting the bluetooth devices stored in phone (especially ones you dont use, but you may need to delete more/all depending on the situation) and add then. This fixes connection issues the majority of the time with very little trouble since rebonding what you need later is a simple task.
Answers & Comments
To identify where the problem is, try connecting another bluetooth device (like another phone, or a bluetooth headset). The other device will most likely connect. If it does, try contacting the manufacturer of the dongle, they will probably have a simple solution to fix it.
If it does not connect to another device, try deleting the bluetooth devices stored in phone (especially ones you dont use, but you may need to delete more/all depending on the situation) and add then. This fixes connection issues the majority of the time with very little trouble since rebonding what you need later is a simple task.