Sorry your going through this.

Would it be possible to return to the old company for one year? May eat some cost on your prepay and may not be the most environmentally friendly decision if your tank is leaking, but needs must.

Outside of that I'd think it's too late to try and do a whole new heat source. Even if you want to switch to something like a wood burner you'd need to acquire the wood, the burner and get it all installed very quickly. Would probably end up running you a similar amount of money you don't have.

Home ownership is always one expense after another. Especially on older homes it seems like it never ends and everything is more expensive than expected. If you can get a personal loan to handle the tank and the plumbing issue I would. Water is something you have to take care of as it will cause more, cascading damage. It's not something you want to let go if you can at all avoid it.