macbook pro magsafe l shape one pin is stuck image

so I'm using my macbook pro MD103 mid 2012 from almost 3 years. My magsafe pins worn out and I gave my charger to replace the wire.

the inside pins of the connecter that attaches to the laptop went inside again in less than a week, then I got the cable replaced again and the same thing happened again. sick and tired I took my macbook to the shop I got it from. they did a whole service and told me that the dust had clogged the fan and it was heating my macbook and thats why the plastic inside the l shape connecter was melting and my pins would go inside. So the service happened and now again after like 4 days one pin has gone inside. Can somebody please tell me what the problem is. I've already spent around more than 45$ on it and nothing has been working out yet.

I'm attaching the pictures below

http://s13.postimg.org/t85lfcc2v/Photo_on_02_02_2016_at_5_57_pm.jpg

thanks you for the help