how to remove promo from directtv stream account

Huh?

First, we're customers like you, not official DirecTV Support. You'll need to call DirecTV Stream at the number below.

Second, if you had a three month promotion that expired, then it's expired. They won't extend that special pricing. 

It doesn't work that way.

Actually, just cancel and move on to another service.

As the customer, it is your responsibility to cancel any promotions, not Directv Stream.  Directv is a company whose purpose is to make money if you forget to cancel that is on you not on them.  To cancel your promotion you need to call customer service and speak to a representative and have them take your promotion off of your bill but you have to do it before your promotion ends or they will make you pay.  They also will not refund you any money if you forget or do not cancel it before the promotion ends so you better cancel before your promotion ends.