How did i test positive for methadone on a instant test and i haven't used any drugs or meds?

Methadone: The quick test (dip stick) is good to get a quick idea. However, its not very specific and false positive results are not uncommon. In an instance like this the specimen must be sent to the lab for confirmation.

False positives: Rapid or screening tests are prone to many kinds of errors, both false positives and false negatives. There are other medications, and even foods that may give a false positive result for many drugs of abuse, including methadone. If there is some legal or social consequence to this test, you need to request that they do "confirmatory" tests, which can sort out between false and true positives.