Wow, it sounds like you have had terrible luck with that piercing.
A keloid and scar tissue are the same thing. A keloid is just very overgrown scar tissue.
I cant see it so I don't know how bad it is, but if it is severely overgrown you can talk to your doctor about getting steroid injections. These injections will take away some or most of the bump, and in some cases will get rid of it completely. It takes about 3 months of injections before you start seeing some results, so if you decide to do this, just keep at it! Unfortunately, there is no home remedy to take away this scarring.
Unless this piercing is a high priority, I really wouldn't recommend getting it done again. With the high rejection rate, it is very very possible that it could happen again. If you do get it again, here are some things you can do to maybe reduce your chances of rejection:
-get it pierced with a hoop, not a barbell. Hoops tend to not get caught on things like barbells do.
-I don't know if you used salt solutions on your previous piercings, but if you did, don't use them with the next one. Salt is very drying and your bellybutton is a very
sensitive area and the slightest thing can cause irritation, infection, and/or rejection.
-Wear long shirts. If you do this, the bottom of your shirts cannot get caught on the piercing.
-Keep it clean! Don't overdo it, but make sure it is clean. Your bellybutton is a haven for bacteria and you want to make sure those nasty little things don't get in your piercing. Clean it twice a day with antibacterial soap for the first two weeks, then after two weeks reduce to once a day. You really shouldn't skip a day of cleaning with your bellybutton.
Good luck and I hope it all goes well for you!