"Buy cheap buy twice" is a perfectly true saying. I take it that you had the secondhand parts fitted by some dodgy character Top as no mechanic with any kind of professionalism or pride in their work would even entertain you. What on Earth they have done can only be imagined, but you are describing the results. There are a lot of clowns out theri and you obviously gave the car to one.
You can only really remedy your problem by fitting new parts. You can buy them yourself at Eurocarparts then give them to a reputable garage or mechanic to fit (not the idiot who bodged it before!). You need a new flywheel, clutch friction and drive plates and a new clutch release bearing. Then your car will change gear happily.
I've never understood why some people scrimp on second-hand items like tyres, brakes, suspension parts and clutches when they then happily spend twice that amount on music systems, woofers and other bolt-on goodies. If you can't afford to fit new parts and maintain your car correctly Top, then you really can't afford the car.