Anonymous“
Shelters is the plural of shelter but in this case it is one group so it is singular, therefor you use offer.
Example I received several offers on repairing my roof. Several plural offers plural
”
Anon, I don't think you quite understand the third person singular and third person plural.
The shelter offers . . . is singular.
The shelters offer . . . is plural
(In your example, offers is a plural noun. The only verb in the sentence is "received" with the subject "I.")