How much would it cost to have someone diagnose where the problem is coming from?
The rising damp industry is full of cowboys. Even the so called established nationwide outfits are cowboys. They are your last port of call.
Do you have extractor fans in kitchen and bathroom? If not your first job is to fit them. You need them even if you don't think you have a damp problem.
Then go outside and look at the wall where you have a problem. Are the gutters leaking and spilling water on the wall? Is there anything which would make the wall excessively damp from the outside?
Then go around your house at damp proof course level and see whether there is anything up against the wall which would allow water in the ground to breach the course. For example soil piled up. If you find it then shift it.
If your house was built in the 50s it almost certainly has a working damp proof course. Do not get a rising damp company in until you have exhausted every other possibility. When they come round be a good host and have somewhere they can water their horse.