Bad Luck!

I think i must have the worst luck ever. I purchased a brand new Viva 125cc Pitbike/Scrambler hoping for plenty of fun with my mates who already owned pitbikes. I knew not to rag the engine straight away so i would just cruise around a little track i made up in 2nd or low 3rd gear not opening up the throttle fully. As i was wearing in my engine on about my 4th day out i heard a massive loud bang and the engine cut out. So i put it in neutral and tried to kick it over, but there was no pressure,my kick start jus went down as easy as feather. Then after a while the pressure was to much and no one could kick it over. So after retreating home i left it to cool down. i tried about 1hour later and it kicked over. I sat there wondeirng what it was when yet again sure enough it went again. So i took out the engine popped to daves and sure enough the engine had seized. So £400 down the line i had a brand new Xsport 125cc sitting in my pitbike. Yet again i took it slowly and yet again on roughly my 4th time out sure enough it has gone again. Please could you give me any ideas on what might be wrong. PLease no one say its my riding because i can ride perfectly well considering i kept a previous pitbike for 1year with no problems with the engine.