"Paid £435 for nothing!"

I have been diagnosed with my condition twice. I got tired of being tossed around by NHS [scheduled and cancelled my treatment twice, no explanation given] so in desperation I called this clinic to try and get a treatment privately. I have made it clear that I know what's wrong with me and am looking to get treatment on the day. Making an appointment, I understood that I will either pay £250 and walk away with nothing, or £400 and walk away treated. I was willing to take that risk to get rid of this long-term condition.

The appointment was late, so off to a bad start. I paid £250 and explained my condition to the doctor and answered their question about cancer check ['I've had it, I don't have cancer']. I also specifically told them that I'm poor and to warn me before doing anything that will raise my bill.

Ignoring that, they asked me later to undress for a procedure. Afterwards they told me that I have this condition and no cancer [information I have given them beforehand] and that it'll be extra £100. I got angry, but trying to be an adult I bit my tongue and left the hospital peacefully, promising to pay.

That wasn't enough though, as few days later I got an e-mail that the price they told me was wrong and it's actually £185.

At this point I was furious and send them an angry reply, but they didn't get back to me for 9 days! Today I send them yet another e-mail, asking for clarification in price [100 or 185?] and bank details so that I can pay it off and be done with them. It still got worse, somehow, as they seem confused with their own system of splitting the bill into 3 payments, and now it seems I'll be getting £15 back and then another bill for £100?..

Point is, I wanted to pay £400 and walk away cured, and they want more than that for giving me a third diagnosis, which is not what I went there for. A waste of time and money. If you do go there, make sure to ask before every procedure 'Wait, will it cost me extra' and 'What exactly is this for?'.