Refusing refund

We booked a flight for two pensioners, after booking the lady went to the doctor only to discover that she cannot fly due to her illness, if we knew she couldn't fly we wouldn't have booed. I then tried getting a refund as we had a doctors letter and everything but Travelstart is just refusing to help. To top it all off we requested to change the details and rather fly down to them but they gave us a ridiculous amount on top of what we paid... Lesson well learnt to never book with Travelstart ever again