The reason for persistent acidity should be looked for and diagnosed. The most common causes are H. pylori infection and GERD (gastro-oesophageal reflux disease. In GERD, the valve between the food pipe (oesophagus) and stomach does not function properly.
In H. pylori infection, there are several therapies available involving acid suppressants and antibacterials. The treatment of GERD includes the use of acid suppressants such as omeprazole or ranitidine sold under different brand names and ultimately surgical fundoplication, if necessary.
Drugs, particularly Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) such as ibuprofen, diclofenac, naproxen also cause gastro-intestinal disturbances including acidity. Hence one should avoid using them.
Lactobacillus acidophilus/lactis, Streptococcus thermophilus, Streptococcus lactis are all good bacteria that are used along with antibiotics. They are ingredients of many branded supplements. They are not likely to be of much help in reducing acidity. Curd is helpful because it neutralises acidity.