How To use Mikrotik with proxy server

Hi All
I have mikrotik 6.28 server and it was working good but our isp
Changes his setting and give us a proxy server with port
Instead of direct gateway.

So I need to change mikrotik setting to use these ISP Proxy settings

My Mikrotik setting is very simple as
one wan interface
One lan interface
gateway
dns
webproxy enabled
3 nat rules
If settings is needed I can send it


Please help