They are both likely responsible. So, you can write to both to demand repairs or reimbursement for the repairs. The internet company's deal with your tenant is not binding on you since you did not sign it. The internet company may have had the tenant's permission, but without yours, the internet company does not have much of a legal leg to stand on.
Get an estimate to repair the damage. Make sure that you take photos of the damage. If not too expensive, you may consider making the repairs and then making claim against the internet company and your tenant. If less than $10,000, you can sue in small claims court. But before you sue, write a letter by certified mail to the internet company and your tenant to demand payment for the repairs. You can use the letter as evidence in your suit, if you have to file one.