I rarely ever get Mixed Up with Coke. My ratio with that and Grab Your Ballas is about 1/10.

You just have to keep trying to call him.

I'm a level 80 BTW so maybe that makes chances of getting it worse.

My missions for martin was locked til i got invite to a mixed up with coke and ever since that mission when i call martin all i get is mixed up with coke and tbh with you its not fun i would like other missions now..

Call Martin, request a job, then when he gives you the job go to it on your phone and press X to delete the message...then wait
3-5min in the same session until you can request another job. He should then give you something different, repeat if necessary.

Once he gives you a job, he will continue to give you the same one even if you beat itjust do what I said above and it should work as that's how I get different jobs from him. Just make sure not to do a mission in between waiting for you to be able to request a job again or it'll give you the same one, and make sure to be in the same session.
If that doesn't work then Idk why, but I hope I helped.