How can I stop long sms being converted to mms on uk s7

[AC Question]

My partner has just bought a galaxy s7 and when sending long messages for work, it is converting it automatically to an mms which she is getting charged for. I have searched through setting for and option to stop this but cant find anyrhinf. I have also seached the internet for answers and not found anything definitive.
My s8 doesn't do it......
Thanks in advance

 

[anon(238680)]

Welcome to Android Central. There is a 147 character limit for SMS, it's supposed to just be used for short, quick posts. Can't you use email, or does that costs also?

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