dsl mbps speed change.

Nobody here can answer that question. You'd have to put in a work request to AT&T to have them check your line from the street to the DMARC on your house. 

Also in case you’re not aware, it’s not the distance to the local cabinet that matters, but rather how far to central office.  
Regardless, there are easy ways to test speeds to your gateway or have Att do it.  And if a technician dispatch is needed as @OttoPylot said, only they can do it, not forum customers like us which mostly support this forum.