Re: Can I get you to do Morrisons as well?
Actually it's a breach of the data protection act/GDPR for them to knowingly hold incorrect information too.
"(d) accurate and, where necessary, kept up to date; every reasonable step must be taken to ensure that personal data that are inaccurate, having regard to the purposes for which they are processed, are erased or rectified without delay (‘accuracy’);"
Also given that it is your personal data (the mobile number) that they are processing without either consent or in fulfilment of a contract it is illegal for them to process that data too.
Your best bet to get this things resolved is to write an email reminding them they are processing your data illegally to firstname.lastname@example.org