cannot get not apple id

Im a bit concern as i have have changed my password to log into my apple account. on my phone its okay but when i try to log into mac it states it incorrect and doesn't recognise the changes, so i go an change the password again putting in a new one and its says it been used before. its clearing seeing that im making the changes but not allowing me access. this is seriously frustrating and thinking of getting rid of this mac and iPhone because of too much security and falser to keep changing passwords i cannot remember.