Lost clients

hi

can you give me some advice I opened a salon one year ago and I have noticed a lot of clients have not returned ! I have done lots of marketing with texts or emails offering discounts etc .I am worried the ones that havent come back are because they have been unhappy with there colour (we only have one colourist ,cant afford another one and also find it hard to get one thats good!) or service, I do not colour and we have had a lot of redos in colour .I definitely think this is down to alot of it .Our technician has only just qualified and hasnt got anyone to give her advice if it goes wrong!

What would you suggest I do to entice these clients back and mainly I want to why they havent back .I was thinking of sending them a letter and free service ?