I'm not a lawyer but please don't let this assholes successfully threaten you!<p>At the opposite I think that you should counteract and ask them to stop using the trademark Ivy even as unregistered as their product would abuse of your 'product name's that is well known.<p>If you look at it, they registered the trademark just a few days ago:
<a href="https://trademarks.ipo.gov.uk/ipo-tmcase/page/History/1/UK00003521605" rel="nofollow">https://trademarks.ipo.gov.uk/ipo-tmcase/page/History/1/UK00...</a><p>On your side, there is even the history of pypi release history showing that you used this name for multiple years.<p>If I was you, I would also fill a complaint to the trademark office to have their trademark registration cancelled on similar grounds that they tried to register a name that was already existing and in active usage for a long time before.<p>Special note to add that really they have no shame of themselves to try to steal for them a common word and first name!