Can you just check that you are not staying at the Merlin Beach resort, rather than Patong Merlin Hotel. As Patong Merlin Hotel, doesn't have pool access rooms. They do have pool view rooms, but to access the pool you would need to clamber across the balcony rail and across the garden bed, not exactly what I would call pool access.
However, Merlin Beach Resort, does have pool access rooms. The pool is shared among the other guests, but it is separate from the main pool. Jim