I invested 50,000 in a company with a payback at 1500 a mon. This was to start in June 2016. They have missed 7 mo.payments . What can I do?

It's not clear to me whether you invested in the company, as you first say, or loaned it money.  If you loaned it money and it has breached the loan contract, you can sue it for breach of contract.  If you invested, assuming that there was no fraud, waste or other wrongdoing, you may be out of luck.  There is never any guarantee that an investment will make money.