Hi Zoojar,

Don't forget to insert a 12V rated Zener between the 12V power supply and Pin 9 of ULN2003 (arrow/anode goes toward ULN2003). As I can see, this is a typical problem caused by the EMF kickback (i.e., reverse current from the coil when the relay is turned off). Adding a Zener should solve such problem.

Good Luck,
Oliver