Letting agent, can I claim back ?

[jobaby1]

I was hoping for some advice, I previously rented a property with my mother through a letting agent. I moved out & was taken off the tenancy agreement when my mother’s partner moved in & was added. They moved home but still with the same landlady & letting agency. Around 2 yrs later they split up so I moved back in to help my mother with the rent & paid it out of my account, we spoke to the agents who cleared it with the landlady and advised I would be added to the agreement & her Ex-partner would be removed however we did not get a new tenancy agreement (it was a rolling agreement) and is has now come to light they have lost the tenancy agreement. The issue is that when I moved out again 2 yrs later & my mortgage company applied for confirmation that I had been a tenant but they would not confirm this and would only state I was paying on my mothers behalf which was not true, due to this I could not get the mortgage & had to get a sub prime with an extra 2% interest plus approx extra 2/3k deposit. I have had it suggested that as they did not have me as a tenant or anything in writing to state I was paying on my mothers behalf that I could try to claim back the rent paid as there was not agreement between us, would this be something that legally I could fight for ?