Last Friday was the last day Customs could hold the cereal - unless Sanitarium filed to the High Court.
On Monday, A Little Bit of Britain received notice Sanitarium had taken the legal action it hoped to avoid.
Now it will be months before the court decides if Weetabix will be back on the shelves.
The business is working with lawyers to file a case before the cut-off date on September 21, store co-owner Lisa Wilson said.
She will then wait for a High Court date.
In the meantime, a Givealittle page started by a customer aims to help pay for the legal fees, and a petition to 'Free the Weetabix' has almost 1000 signatures.
The seizure prompted a hashtag on social media #freetheweetabix, and British newspapers are also reporting on the branding row.
Wilson is optimistic Weetabix is not a trademark infringement under the Trade Marks Act 2002.
"We would have to confuse, deceive or pass it off as Weet-Bix [to classify as a trademark infringement] and we are definitely not doing that by selling Weetabix in our little British store and website," she said.
"We go through a pallet of 300 boxes every eight weeks. Think of how much Weet-Bix Sanitarium is making and selling daily. How can they say it's affecting them?"
It was also a matter of principle, Wilson said.
"We don't want them to come along and bully small businesses about what they can and can't sell. But it will come down to what the judge says on the day."
During the Weetabix drought, Wilson is trying to feed her son Shredded Wheat - another British cereal.
"He's not so happy about that. He is only 2 and he spits it out."
Sanitarium has been approached for comment.