Vehicle Repossession Legalities Explained

I purchased a vehicle four weeks ago from a friend that i help do chores at his home and property. He sold me a vehicle for $*,*.* and set the monthly payments at $*.* which he wrote down on paper and i signed. He told me on months i couldnt pay the entire *.* to pay what i could and months i could afford to pay more than *.* so i could get it paid off sooner but didnt put all that on the paper i signed. I draw social security disability and on payday */*/* i was only able to pay him $*.* due to moving home with my wife after we reconciled. I ask him on */* when i paid him the *.* could we change the payment to $*.* every month. He said no and that i had till */*/* five days to pay the remainder of the payment which would be *.* or he was coming to pick the vehicle up. I paid him *.* when i signed paper he signed titleto me with him as lien holder so i could register it and get my tag which i have done. He calling multiple times a day asking do i have the money, comes by my house every day asking do i have the money and he coming to pick vehicle up */* even following my wife around town going by her friends houses asking is she there telling them she owes him money and she has nothing to do with this at all. I live in calhoun county Mississippi can he legally come pick vehicle up and can he keep harassing us especially my wife

I signed paper stating payments were *.* i was only able to pay *.* this month so can he come pick vehicle up since i only paid *.* instead of *.*

Thank you so much for your time