I complained at the time and certainly made my feelings felt, but as cancelling would have meant losing the flight, transfers, insurance and, more importantly, my week's annual leave I grudgingly accepted the move.
I was not happy with the quality of the hotel I was moved to. To put it bluntly, if it happens again, I will cancel and take the hit.
On my return, I put in a complaint to the agents, mostly because of the un-refunded difference in prices, but I included aspects of the hotel which I was not happy with.
Below are two screenshots of the relevant hotels, the departure date is the same for both, 3 weeks ahead, I do not have screen shots from the time of booking as I did not ever envisage needing them! But you can clearly see the difference.
I had booked the Maritim and was moved to the Santa Monica. I always select a double/twin for single use as single rooms everywhere abroad are notoriously tiny.
According to ABTA rules, travel agents have to respond to complaints within 28 days. Despite asking for more information to support my claim, (why, they moved me, they know the difference in price) the travel agents have failed to do this.
I have moved to the next level in my complaint, I have sent notice of my intention of going to ABTA, I just have to give more time for the agents to respond.
I will keep you informed.
Update
Today, 31st July, I had a reply from the travel agents, as it wasn't their fault I was moved, they were offering me £50 as a goodwill gesture.
As there is such a difference in price to the customer, I feel it is safe to assume that there is a corresponding difference in price to the travel agent, and therefore I should receive the full difference back, at least.
If there isn't a difference in price to the travel agent, then why is there such a disparity in price to the customer?
I have forwarded the offer on to ABTA for their consideration.