Waltz impossible

I need some advice about unexpected cost on a project that I hired a landscaping company do, thank you in advance: 1. These two retaining walls in the photo were added in the middle of a job, it costs £1450 for the concrete blocks(1st photo , not sure if porcelain cladding is included or not) and £550 for the the timber (2nd photo). Reasonable? 2. There are two other concrete block planters that is now lower than the original agreed height, instead of 0.6m, now is two blocks in height (215+215), and we also agreed porcelain cladding on these planters, now these planters are lower therefore less work and should cover the cost and material for the above extra work in 1. ? 3. A competent landscaper should have known where retaining walls are needed before they start the job (sloped garden), and shouldn't need to decide in the middle of a job and charge extra, am I right?