How can companies stop losing customers?

Stay in contact with your long term customers 

Always give value to your customer 

keep check on the buying behaviour of your customer

keep innovating to create more and new customers

Most of all deliver what you advertise about your product it will give quality 

Its depend upon nature of business, if you are industrial supplier then you should fulfill the customers required materials though it is not in your product range. You have to buy from local materials sources and provide it to your customer. Otherwise, offcourse customer will go to another place where he can get his complete requirement.

i think that these companies does not meet the customer needs ,this is the reason for losing customers