Is this trademark too descriptive? Can they stop me using the phrase when describing goods and services offered by my business?

I own the website www.printypets.com. I recently received an email from the owner of the trademark “print your pet”. I was using an image in an advertisement that used the phrase “print your pet on a blanket”. They demanded I take it down and asked for my details so their lawyer could send a letter of demands. I don’t know how to respond. I am simply describing the service offered on my website. Other website do the same thing: • www.mypetprints.co • www.petcanva.com • www.popyourpup.com • www.ilovepaws.com And many more I do not see how I am not allowed to use “print your pet” when used in a larger phrase describing some of our goods and services. I’m in no way trying to confuse people or impersonate the Print Your Pet website at all. I’m just describing what we do. I would argue that “Print Your Pet” is too descriptive. It is a supplemental trademark if that has any significance. I’m looking for some thoughts and advice. Thank you