renault megane 2003?

Just had MOT on above vehicle and unfortunately it ass failed. Suspension spring snapped and rear brake pads worn. Anyway got parts and fitted myself. Spot on. However, tonight went to apply handbrake and it gave like it snapped. On further investigation the brake calipers cables both look good. However checking on the inside of my vehicle behind the handbrake lever the 2 cables look different lengths therefore when one is under tension the other is loose and therefore coming out of its location and handbrake is inoperable!!!!!!! Why as this happened after new brakes fitted as they were fantastic yesterday. Could they have streched?