My cellar has a horrible smell and one of the walls feels wet. What is the best solution for it.

There are many different solutions for this. Some cheap, some expensive. Best to post job on here and get some tradesman to assess job and provide a quote

firstly remove all materials that will soak up moisture and create odor like cardboard's, clothes, carpets etc. Clean out any debris. Remove the render from the damp wall and re render with a tanking system. DSL UK