Pet Shop Problem (Small claims court)

Hoping i can get some advice please as not sure how far to take this.
Its quite along story so will try to keep it as short as possible.
Visited a local pet shop and decided to buy a guinea pig which was a male we called it Boris. Was given lots of info in the store from the assistant which turned out to be wrong.
Just over a week later we returned to the store to get him a companion as we found out they really need a friend. We told them we needed a male as we already had a male so they checked several times and they assured us it was a male as they don't sell females so we bought it and took it home We called this one Peanut.
After a week we introduced them into the same cage and we thought that would be the end of it.
How wrong that was. After about 10 days we started to notice the Peanuts fur was falling out around its nose this carried on for a few days so we decided to pop it into the vets to have someone look at it. Was told it was Hay Mites and was given treatment, the fur loss turned into sores and didnt seem to be getting better We had now also started to notice Peanut was getting fatter.

Boris the first Pig was also now losing his fur, so back to the vets for another check and was told it was Ringworm which had also been passed onto Boris and Peanut was infact a Female Guinea Pig who was pregnant.The Vet told us that judging by how pregnant she was she was actually sold to us already pregnant. He also told us that as Peanut was pregnant she couldnt be treated for the ringworm as it could effect the babies

After speaking to a few people we decided to call the pet shop and spoke to the manager only to be told they do not sell females and we must be mistaken, he also said all guinea pigs are treated for ringworm by the breeders. The manager said he would contact head office and get back to us which he did. He said head office told him to offer us £50 and a tin of ringworm treatment, but as the vets bills had already gone over that amount i refused, we also had to think about the cost involved to get Boris Neutered.
By now Peanuts face looked very sore so after doing some research on a forum we found a vets about 18 miles from were we live that has a vet who specialises in guinea pigs so we took them both to see her.

She gave us treatment that was safe for pregnant guinea pigs and told us Peanut was due to have the possible three babies over the next week or so she also said Peanut was pregnant when we bought her and the ringworm more than likely came with her from the pet shop which i have in writing.
I wrote to the pet shops head office and told them what had happened and they told me to send any receipts i had and any reports from the vets and they would consider what to do.

A few days later we woke to find quite a bit of blood in the guinea pigs cage so went back to the vets again to have her checked the babies seemed ok.

At the end of the week my wife returned home from work to find peanut had the three babies and they were all dead she was also acting very strange which we assumed was because of the ordeal she had been through.
No change the following day and by Sunday she was getting worse infact it looked as though she had a stroke. Back to the vets again but as it was a sunday it was Emergency Vets (expensive), gave her medication and we left, anyway no improvement still she now appeared to be blind and couldnt hear anything so after a few more trips to the vets we managed to get to see the vet who deals with guinea pigs again after a quick examination she told us there was another dead baby inside her still and it was poisoning her.

This poor Animal had gone through so much so we decided to give her this last chance and go with the operation. Was told it was a huge risk as she was very weak and very young.
She survived the operation and started to get better, we had to feed her via a syringe through the night and she looked to be improving, nearly two weeks after her op she went down hill and refused to eat and we decided it was time to put her to sleep. We had been through so much trying to get her better.
All the vets bills added up to over £700 we sent everything to head office and they basically said nothing they could do.
After lots of letters backward and forwards they told us we signed a pet release form saying they do not guarantee the sex of animals and any vets costs must be confirmed by them in writing before seeing a vet.
I have records of all the receipts and all letters sent backwards and forwards. I have also sent them a letter before action letter and told them im willing to use Alternative Dispute Resolution.
They have now increased their offer to £75 and told us we did not take the guinea pig back within 7 days and they also said we did not give them the chance to let their vets see her. (None of these were ever mentioned)
Started small claims proceedings and paid the fees. Today i had a reply from the court saying the pet shop had rejected my claim and they now wanted to use the Free mediation service.
Am i wasting my time and money citizens advice told me they are in the wrong and im claiming consequential loss as i was sold something that wasnt as described and the costs i incurred are a result of that.:(