Why are you using Mangle anyway?
I want to be able to use the office connection as the main internet connect for the mikrotik LTE device, send all traffic from the LTE down the tunnel to the office connection.
You want to send all traffic through the VPN-tunnel am I right?
It seems to me that you have build an overly complex set-up, which is also hard to troubleshoot. I followed the documentation on the Wiki: https://wiki.mikrotik.com/wiki/Manual:I ... -Site_L2TP
add local-address=192.168.100.6 name=map_bram remote-address=10.9.5.1 routes=10.9.5.0/24 service=pptp
add distance=1 dst-address=0.0.0.0/0 gateway=ISP Gateway IP
My DNS-setup isn't really relevant. It just works, but in my case I have two Windows AD-DNS-servers providing the DNS-services.
On the remote end I've created the VPN tunnel as a client, making sure the add default route option is checked:
add add-default-route=yes connect-to=<office router Public IP> name= profile=default user=map_bram
This will add all nessecary routes for your connection and will send all traffic trough the VPN-tunnel