Question regarding fonts and commercial licenses

Hi r/legaladvice,

I'm a graphic designer that's been working on quick-turnaround logos for music artists on a TV show with the aim to broadcast them within the coming days.

I was quite meticulous when choosing fonts for these logos, and ensured that they were commercially usable to avoid any legal issues.

A particular font named Antro Vectra looked good, so I created a logo to show the client, knowing that it could not be used commercially until contacting the author (as per the DaFont page).

I then emailed the author, who agreed the font could be used commercially for a band/singer (and he did not mention any other restrictions). He said I could pay what I felt was fair, so I transferred him £15.00GBP. He told me he would send the license over within 24 hours of payment.

Due to the urgency of the work needed, the author failed to contact me to acknowledge payment or offer the license until 38 hours after the payment was issued. By this point, I had already sent the logo to the client as the author had previously agreed it could be used for a singer/band commercially.

When the license was sent to me, it came with previously unmentioned T&C's including not being able to use the font for TV/Broadcasting. Had this been relayed, I would not have used the font. The author is now claiming I owe him substantially more money otherwise I am breaking the law. The logo is already in use and cannot be revoked, leaving me worried about the legalities and the author changing conditions after payment.

If a product has been sold without terms and conditions, surely they cannot be then added after payment has been accepted.

Am I within my right to claim that the conditions were not explained before purchase? Or am I facing a legal battle which could potentially cost me much more money than I own?

I'm also UK based. Thank you in advance for your advice.