You could follow the downgrade suggestion from @Santhosh in your other more relevant topic: Can't Install Dahdi with FreePBX 17 - #4 by Santhosh
Appreciate the PRI discussion, which is particularly relevant to users who do not want to deal with directly connecting their FreePBX systems via IP access to the internet – preferring instead the TDM break – but this is perhaps tracking off-topic, so, should we move relevant posts to the “Industry” category instead ?