Today I attempted to change the bottom bracket on my old mountain bike. Whilst I was unscrewing the non drive side cup I came across a problem. The thread had gone and was just turning round and round and not coming out. Eventually I managed to get it out but now when I've put the new one in I can't get the cup to screw in properly, the thread inside the frame is damaged. Is there anything that can be done or is the frame now ruined?