Non refundable deposit help

Kitchenfitter4766

Looking for some advice please
We paid a £300 deposit on a male puppy after some thought as we have a lively other male dog decided it would be best to have a female. Checked the ad and the sellers still had a female so called them to ask if we could swap, the lady said yes straight away so we were very pleased. 
Then the man said no i sold her last night so we said we would happy pay a little more (£100) but they sad no she was sold
Within 10mins they texted back saying we can pay another £580 more for the swap I couldn't believe they were now taking advantage and trying to rip us off - even changed the ad saying boys only left
We declined and said we will decide whether to cancel or not
Again with 10mins they said they would accept another £150 instead of the £580, we did not reply straight away as decided to have a good think  again they then texted offering a straight swap with no additional costs. We declined feeling they were definitely try to rip us off in the first case
They have now advertised the puppy online for £150 less than what we were going to pay and have told us that our deposit is non refundable
Do I have any kind of chance of getting our deposit or part deposit back
Any advice is appreciated 

unforeseen

I hope, with prices you are quoting that those dogs have got good solid pedigrees checkable with the Kennel Club

Or is it one of these mongrel/crossbreeds that have the stupid fictional breed name of cockapoo or other concatenation of two breed names

Katiehound

and sorry, buying from an advert.........when they are reputable breeders around and rescues too....
I don't think you have any chance of getting the money back because you changed your mind. ( and I guess you are dealing with very suspect sellers / puppy farmers who are operating under the legal radar anyway) Otherwise you might have tried the small claims court route.