[ASK] Funny ISP with quota

Hi everyone, im wanna ask for script,
My isp broadband so funny, its use quota, after used 2 tera speed drop to 60%
I have 2 connection with same isp, this how look like my route:

RouteISP1 distance=1 comment=aaa
RouteISP2 distance=2 comment=aaa
State=enable

RouteISP2 distance=1 comment=bbb
RouteISP1 distance=2 comment=bbb
State=disable

So my question is, how to change every date 15 every month, ISP with comment bbb auto enable and with comment aaa disable, and back aaa auto enable and bbb disable on date 15 next month, any coment and answer will be appreciation,
Thx