Hi,
There is a router(cmts) between users and mikrotik. Users get ip address (cm etc) from provisioning server. Then they authenticate with pptp protocol to get their internet access. As there is a router between Mikrotik and users I cannot use hotspot or pppoe. There is no option for cmts to run in bridge mode. Below is the image. Is this possible

Its possible, but it doesn't make a lot of sense. Why is the CMTS not talking directly to the RADIUS server? Many of the CTMS servers I have encountered did have a "bridge" mode. Have you contacted your vendor and asked them about it? PPPoE makes more sense in this case. I'd dig more into a way to use it.