Third toilet in three months

[Kay Khan]

Tenants moved in three months ago and we have already replaced two toilets in the last two months. I got a call this weekend and my maintenance guys worked on it, saying sewer line is clear but some thing is stuck in the toilet bowl. They took the toilet out and manage to get a fridge magnet out but unable to clear the toilet. How should I deal with it. Have tenants sign a responsibility letter and bill them for third toilet? Please help.

Thanks in advance.

Kay Khan