We have the rights for social media services. We don't care about people using it as descriptive text, we care when they use it to market advertising services.
It's just a common phrase you don't want other people to use in the same context they have been using it in for a long time.
It seems in fairly widespread use even for that use case.
This seems analogous to a company trying to trademark "Skip the lines" when advertising an online store.
Also, is "Spread the word" really the "most integral part of [y]our branding and marketing"? The phrase doesn't seem inherently or distinctly creative, nor can I really see a second meaning the immediately invokes your product/services. Surprised you were granted the trademark at all.