Does s.196 LPA 1925 apply to notice of assignment served whilst in proceedings

[Sweets]

My company is the defendant to a claim for early termination fees. By way of a business purchase agreement, the original claimant's who were party to the subject contract assigned their claim to the new claimant. The new claimant claims it is a legal assignee because they sent notice of the assignment in March 2020. The claimant's solicitor filed an unsealed certificate of service dated November 2020, to substantiate service of the notice. They also sent the notice of assignment in June 2020 by email attached to a completely unrelated documents and so was totally overlooked. S.196 LPA 1925 says that the notice has to be received at the business (postal) address. We deny receiving the notice. The claimant's have now made an application to substitute itself as the claimant, with the intention to enforce the subject contract. It is our position that the new claimant's are only equitable assignees because they didn't serve notice in accordance with s.196 LPA 1925, could someone kindly provide some direction please. Also could anyone give their interpretation of s.196(6) which states that, "this section does not apply to notices served in proceedings in the court. Thank you