worst Network Coverage

Firstly the is no customer service team to help with quarries and the network coverage from my house is useless and on the website it said i have 4G coverage and yes it was there the first month i bought the sim but now its takes more than 3 seconds to send a whatsapp message and i can not be on a zoom call for work related staff and the reason why i paid for the unlimited data plan that i can't even use to do anything with