Gear troubles

So a few months ago my car wouldn't go into gear, it literally happened one morning after having no run up problems or gear problems at all, so took it to my local garage and it needed a new gear box and clutch. After the 1st week of having it back although the gear stick glided smoothly into gears. It kept bouncing back out of gear. I took it back and the owner apologized that the gear box it was replaced with was no good and they replaced it with another. After collecting my car for the 2nd time he explained to give it a few weeks it may feel a little different. I gave it a few weeks but it never seemed to like going into 1st or 2nd gear. It would crunch or just not go into gear at all, particularly into 2nd gear when slowing down to the point where I would have to come to a stop to start again in 1st gear because it wouldn't lower into 2nd. I've taken it back again and this time they have said it could be the gear stick that's worn over time. However including my original gear box before it needed replacing I never had this problem not even with the 1st gear box they 1st replaced that was no good. It still smoothly went into the gears it just bounced back, its only been this 2nd box they have replaced that it doesn't like going into 1st or 2nd. Could it really be the gear stick that he is saying? Surely would I not of had this problem with the 1st gear box they replaced that was no good. As despite it bouncing back out of gear it smoothly went into all the gears. Not like this time where the problem is only 1st and 2nd. I understand the stick may wear over time and could understand If I had 3 gear boxes over 3 years and it happened with every box, yes we could say its worn over time but surely if its had no problem moving into the last 2 gear boxes within only a few months can he now really say its the stick that's the problem when its only been this last gear box that the stick is struggling with going into 1st and 2nd?
If it is the gear stick worn as he's saying. Is it another costly replacement or does it sound like the problem is still the gear box itself? Any advice would be much appreciated.