Sorry to beat the same old drum again, but so much can be avoided by having a legally binding contract. You are a professional. You are in business. Get a contract drawn up (See the Independent Medical Transcriptionist for samples).
When I looked into working for the VA Domiciliary here as a home worker, I got a copy of their contract, actually 3 copies of their contract, all 35 pages of it. Everything was spelled out, down to the last period and comma, when carbons were to be used, how each type of report was to be logged, etc.,etc.
After my friend was suddenly dropped from an account she had had for 11 years (showed up to pick up tapes and they told her they had hired the business manager's niece), I decided to CMA and put together a contract.
So many of the problems I had had before then disappeared with the implementation of a contract. I refused any new clients unless they would work on a contract with me. One doctor even looked at me with astonishment, as though a chair had walked and talked, when I insisted on a contract.
My contract included payment clause -- with a set amount for any payment later than 10 days from their receipt of my bill, with appropriate escalations, including legal for outright nonpayment, as well as denial of further services until outstanding amount had been paid.
Believe me, I may have lost a few prospective clients, but in the long run I didn't get ulcers and didn't get stiffed either.
When I was teaching MT students, I gave them copies of my current contract to use as a guide and emphasized to them that if they were going into business as an MT that they should conduct themselves in a business-like manner.
Look over the samples in the Independent MT, and I am sure there are others specific to MT business online too. Talk to your local small business advisors, contact the SCORE people. You would be amazed at how much help there is out there for you.
Sorry you have this problem, been there myself, seen fellow MTs there too. Hope it all works out for you.
Nancy 