£4,000 legal bill for S21 eviction that i won!

Hi

I was evicting a tenant via an S21 eviction

I got the first eviction, which the tenant defended with a solicitor and managed to get out of it, due to a small error on my s21 form

I re sent the s21 with the correct date and the tenant was evicted last week

I have now received a letter from his solicitor requesting £4,000 legal fees

I was shocked to say the least, after i did manage to evict him

I've done several s21 evictions and never had to pay any solicitor fees

Are they allowed to claim this amount off me?

How do i contest this £4,000?

Please help, thanks