Hi all, really hoping I can get some advice please,

In January we booked an all inclusive holiday online with Thomson. We paid extra to fly premium club as I am quite a big person and it wouldn't be practicle to fly long haul in normal seats. We booked these particular dates specifically for this reason.A few days later my wife (who works in the airport) went to the Thomson desk and spoke with the supervisor who then allocated our seats 5D & 5E going and also coming back. The seats are either side of an aisle as otherwise we would not have been able to sit together as though he only other available seats were single seats apart from each other(confirmed by Thomson supervisor)Yesterday (Sunday afternoon) I received a call from someone at Thomson to say that they were downgrading my seats as they had double booked 'due to inventory problems'.I was told that the 'seating team' in the escalations department had a meeting at which this had been decided.I tried explaining this was not a viable option but was basically told I had no choice and they would be refunding the cost of the premium seat upgrade only.However I have not agreed to this as I would not be able to travel under these circumstances.I asked the name of his manager and he wouldn't give it to me, I asked for their contact details so I could speak to his manager but I was told that this would not be possible as his manager is not "in a customer facing role".He would not even give me his direct contact number and when I tried calling their emergency number they told me it is not possible to call the escalations department directly!.I then received two emails titled "Booking Amendment Confirmation"In which Thomson thanked me for my booking and the amendments which were set out in the email!. I have not agreed to, nor confirmed any of these changes, in fact I clearly objected.Is there anything I can do please?