My ex husband had custody of our son he has problems a year ago he dropped him off stayed long enough to unload his stuff now he wants him back he said he didn't want to go so the cops said he didn't have to they took him to Walmart and never came back what can I do

'now he wants him back he said he didn't want to go so the cops said he didn't have to they took him to Walmart and never came back.. '

Can you please re-write who each of the different 'he's are for each event?
It sounds like the cops left your son at Walmart. But probably they met your ex at Walmart so that your son wouldn't cry and fight, sorry. There is nothing you can do unless you want to go to Family Court and try to fight the custody arrangement.
You might have a reasonable chance for at least a shared arrangement - but we don't know why the court decided what they did originally.

I agree with Joypulv, the passage is confusing. I was about to ask why the ex was crying that he didn't want to go; and why the cops took the ex to Walmart. But she gave what is a probably an accurate translation..

When he dropped the child off, did you go back to court to modify the custody agreement? If not, then you left yourself open for him to take the child back.

You need to detail what current court orders exist.