The seal is:

Shengji

"Shengji" purple clay teapot is produced in Yixing and is a product of the purple clay "Jinding Trademark". It was founded by Hu Desheng around 1911. The "Jinding Trademark" was registered until 1937, when it gradually declined during the Anti-Japanese War.

I wonder if your pot belongs to this "Shengji".

Hope this helps.

Note: The information comes from the Internet