Cunningham Real Estate not living up to their promise

We bought a property trough Cunningham Real Estate and they promised to fully paint the property as there where marks from the previous owner. They said they will buy a 20L and when we came back to them they said they are only willing to buy a 5L of paint as this was agreed with them. The owners husband directly asked me can he go ahead and buy the 20L or did I take the measurements, they owner then after called me and said that I am lying and that he never said he will buy a 20L.

This is one of the worse experiences I have had as I am a man of my word and this is not living up to it and disappointing that they can make promises before they receive the money, but afterwards they are not willing to help anymore.

I hope this helps other people to document everything discussed (Via e-mail or recording etc.) to not go trough the same process as I am currently facing