Workaround on nested async completion blocks from network calls? Without using PromiseKit

Basically I have an existing API manager that is blocking me from going forward. This existing manager is something I should not mess with right now.

This is the gist of my problem. I mean, I can go forward with this way, but it's sooooo annoying. I hate these nested completion blocks. Does anyone have any workaround idea that can solve this? PromiseKit is out of the option.

This is how I call it.

- (void)doEverythingHere {
    [self getDataOneWithCompletion:^(DataOneModel *response) {
            if (response.isSomething) {
                [self getDataTwoWithCompletion:^(DataOneModel *response) {
                    // And call some more of these...
                    // So the nested blocks will never end... and it's ugly
                };
            } else {
                [self getDataThreeWithCompletion:^(DataOneModel *response) {
                    // And call some more of these...
                    // So the nested blocks will never end... and it's ugly
                };
            }
    }];
}

These are the sampl API methods.

- (void)getDataOneWithCompletion:(void(^)(DataOneModel *response))completion {
    [APIManager getDataOneWithResponse:^(DataOneModel *response) {
        completion(response)
    }];
}

- (void)getDataTwoWithCompletion:(void(^)(DataTwoModel *response))completion {
    [APIManager getDataTwoWithResponse:^(DataTwoModel *response) {
        completion(response)
    }];
}

// And 4 more of these API call methods.