I have a DMVPN setup with IPSEC and BGP. The problem is that the default route from BGP is not installed in the routing table so i have to set a static route. This works but is not a permanent solution if the Teltonika is for example not the last router in a redundancy setup.
On your WAN interface, try setting the metric to 352321537 (which is basically [21/1] - AD of 21, higher than EBGP) and let me know if this helps. You might also want to check the neighbor’s weight in the BGP settings.